U.S. patent application number 17/133547 was filed with the patent office on 2022-02-17 for apparatus and method for improving graphics processing performance.
The applicant listed for this patent is Intel Corporation. Invention is credited to Bret G. Alfieri, Abhishek R. Appu, Joshua Barczak, Carsten Benthin, Michael J. Doyle, Holger GRUEN, Stephen Junkins, Sreenivas Kothandaraman, Adam Lake, Won-Jong Lee, Gabor Liktor, Prasoonkumar Surti, Karthik Vaidyanathan, Sven Woop.
Application Number | 20220051476 17/133547 |
Document ID | / |
Family ID | |
Filed Date | 2022-02-17 |
United States Patent
Application |
20220051476 |
Kind Code |
A1 |
Woop; Sven ; et al. |
February 17, 2022 |
APPARATUS AND METHOD FOR IMPROVING GRAPHICS PROCESSING
PERFORMANCE
Abstract
Apparatus and method for efficient graphics processing including
ray tracing. For example, one embodiment of a graphics processor
comprises: execution hardware logic to execute graphics commands
and render images; an interface to couple functional units of the
execution hardware logic to a tiled resource; and a tiled resource
manager to manage access by the functional units to the tiled
resource, a functional unit of the execution hardware logic to
generate a request with a hash identifier (ID) to request access to
a portion of the tiled resource, wherein the tiled resource manager
is to determine whether a portion of the tiled resource identified
by the hash ID exists, and if not, to allocate a new portion of the
tiled resource and associate the new portion with the hash ID.
Inventors: |
Woop; Sven; (Voelklingen,
DE) ; Doyle; Michael J.; (San Jose, CA) ;
Kothandaraman; Sreenivas; (Sammamish, WA) ;
Vaidyanathan; Karthik; (San Francisco, CA) ; Appu;
Abhishek R.; (El Dorado Hills, CA) ; Benthin;
Carsten; (Voelklingen, DE) ; Surti; Prasoonkumar;
(Folsom, CA) ; GRUEN; Holger; (Peissenberg,
DE) ; Junkins; Stephen; (Bend, OR) ; Lake;
Adam; (Portland, OR) ; Alfieri; Bret G.;
(Forest Grove, OR) ; Liktor; Gabor; (San
Francisco, CA) ; Barczak; Joshua; (Timonium, MD)
; Lee; Won-Jong; (Santa Clara, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Intel Corporation |
Santa Clara |
CA |
US |
|
|
Appl. No.: |
17/133547 |
Filed: |
December 23, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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63066799 |
Aug 17, 2020 |
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International
Class: |
G06T 17/10 20060101
G06T017/10; G06T 17/20 20060101 G06T017/20; G06T 3/40 20060101
G06T003/40 |
Claims
1. An apparatus comprising: a tesselator to tessellate an input
patch to a grid primitive comprising a plurality of interconnected
quads, each quad comprising two implicit triangles and sharing at
least two vertices with an adjacent quad; a bounding box generator
to construct a bounding box to bound each quad of the grid
primitive to produce a plurality of bounding boxes corresponding to
the plurality of interconnected quads; and ray traversal hardware
logic to determine if a ray traverses one or more of the plurality
of bounding boxes; and intersection hardware logic to process a
bounding box traversed by the ray to determine if the ray
intersects one of the implicit triangles represented by the quad
which is bounded by the bounding box.
2. The apparatus of claim 1 wherein the grid primitive comprises an
M.times.M matrix of vertices forming the plurality of interconnect
quads.
3. The apparatus of claim 1 wherein the bounding box generator is
integral to the ray traversal hardware logic or a bounding volume
hierarchy (BVH) builder.
4. The apparatus of claim 1 wherein for a grid primitive comprising
N quads, the bounding box generator is to generate an N-wide BVH
node having a child node associated with each quad.
5. The apparatus of claim 1 wherein a bitmask is generated based on
the grid primitive, each bit in the bitmask associated with one of
the implicit triangles or one of the quads, wherein if a bit in the
bitmask is set to 0, the associated implicit triangle or quad is
considered invalid.
6. The apparatus of claim 1 further comprising: motion blur
hardware logic to interpolate between a first representation of a
first implicit triangle at a first time and a second representation
of the first implicit triangle at a second time.
7. The apparatus of claim 1 wherein the grid primitive is one of a
plurality of grid primitives, the apparatus further comprising:
compression hardware logic to identify shared vertices of the
plurality of grid primitives and to store only one set of vertex
data for each shared vertex.
8. The apparatus of claim 7 wherein the compression hardware logic
is to generate an index pointing to an array where the set of
vertex data is stored.
9. The apparatus of claim 8 wherein the compression hardware logic
is to identify one or more shared edges of the implicit triangles,
the compression hardware logic to store a single set of edge data
for each shared edge.
10. A method comprising: tessellating an input patch to a grid
primitive comprising a plurality of interconnected quads, each quad
comprising two implicit triangles and sharing at least two vertices
with an adjacent quad; constructing a bounding box to bound each
quad of the grid primitive to produce a plurality of bounding boxes
corresponding to the plurality of interconnected quads; and
determining if a ray traverses one or more of the plurality of
bounding boxes; and processing a bounding box traversed by the ray
to determine if the ray intersects one of the implicit triangles
represented by the quad which is bounded by the bounding box.
11. The method of claim 10 wherein the grid primitive comprises an
M.times.M matrix of vertices forming the plurality of interconnect
quads.
12. The method of claim 10 wherein the bounding box generator is
integral to the ray traversal hardware logic and/or a bounding
volume hierarchy (BVH) builder.
13. The method of claim 10 wherein for a grid primitive comprising
N quads, the bounding box generator is to generate an N-wide BVH
node having a child node associated with each quad.
14. The method of claim 10 wherein a bitmask is generated based on
the grid primitive, each bit in the bitmask associated with one of
the implicit triangles or one of the quads, wherein if a bit in the
bitmask is set to 0, the associated implicit triangle or quad is
considered invalid.
15. The method of claim 10 a first representation of a first
implicit triangle at a first time and a second representation of
the first implicit triangle at a second time.
16. The method of claim 10 wherein the grid primitive is one of a
plurality of grid primitives, the method further comprising:
identifying shared vertices of the plurality of grid primitives and
storing only one set of vertex data for each shared vertex.
17. The method of claim 16 further comprising: generating an index
pointing to an array where the set of vertex data is stored.
18. The method of claim 17 further comprising: identifying one or
more shared edges of the implicit triangles, and storing only a
single set of edge data for each shared edge.
19. A machine-readable medium having program code stored thereon
which, when executed by a machine, causes the machine to perform
the operations of: tessellating an input patch to a grid primitive
comprising a plurality of interconnected quads, each quad
comprising two implicit triangles and sharing at least two vertices
with an adjacent quad; constructing a bounding box to bound each
quad of the grid primitive to produce a plurality of bounding boxes
corresponding to the plurality of interconnected quads; and
determining if a ray traverses one or more of the plurality of
bounding boxes; and processing a bounding box traversed by the ray
to determine if the ray intersects one of the implicit triangles
represented by the quad which is bounded by the bounding box.
20. The machine-readable medium of claim 19 wherein the grid
primitive comprises an M.times.M matrix of vertices forming the
plurality of interconnect quads.
21. The machine-readable medium of claim 19 wherein the bounding
box generator is integral to the ray traversal hardware logic
and/or a bounding volume hierarchy (BVH) builder.
22. The machine-readable medium of claim 19 wherein for a grid
primitive comprising N quads, the bounding box generator is to
generate an N-wide BVH node having a child node associated with
each quad.
23. The machine-readable medium of claim 19 wherein a bitmask is
generated based on the grid primitive, each bit in the bitmask
associated with one of the implicit triangles or one of the quads,
wherein if a bit in the bitmask is set to 0, the associated
implicit triangle or quad is considered invalid.
24. The machine-readable medium of claim 19 further comprising
program code to cause the machine to perform the operations of:
interpolating between a first representation of a first implicit
triangle at a first time and a second representation of the first
implicit triangle at a second time.
25. The machine-readable medium of claim 19 wherein the grid
primitive is one of a plurality of grid primitives, the
machine-readable medium further comprising program code to cause
the machine to perform the operations of: identifying shared
vertices of the plurality of grid primitives and storing only one
set of vertex data for each shared vertex.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 63/066,799, filed Aug. 17, 2020, all of
which is herein incorporated by reference.
BACKGROUND
Field of the Invention
[0002] This invention relates generally to the field of graphics
processors. More particularly, the invention relates to an
apparatus and method for efficient graphics processing including
ray tracing implementations.
Description of the Related Art
[0003] Ray tracing is a technique in which a light transport is
simulated through physically-based rendering. Widely used in
cinematic rendering, it was considered too resource-intensive for
real-time performance until just a few years ago. One of the key
operations in ray tracing is processing a visibility query for
ray-scene intersections known as "ray traversal" which computes
ray-scene intersections by traversing and intersecting nodes in a
bounding volume hierarchy (BVH).
[0004] Rasterization is a technique in which, screen objects are
created from 3D models of objects created from a mesh of triangles.
The vertices of each triangle intersect with the vertices of other
triangles of different shapes and sizes. Each vertex has a position
in space as well as information about color, texture and its
normal, which is used to determine the way the surface of an object
is facing. A rasterization unit converts the triangles of the 3D
models into pixels in a 2D screen space and each pixel can be
assigned an initial color value based on the vertex data.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] A better understanding of the present invention can be
obtained from the following detailed description in conjunction
with the following drawings, in which:
[0006] FIG. 1 is a block diagram of an embodiment of a computer
system with a processor having one or more processor cores and
graphics processors;
[0007] FIGS. 2A-D illustrate computing systems and graphics
processors provided by embodiments of the invention;
[0008] FIGS. 3A-C illustrate block diagrams of additional graphics
processor and compute accelerator architectures;
[0009] FIG. 4 is a block diagram of an embodiment of a
graphics-processing engine for a graphics processor;
[0010] FIGS. 5A-B illustrate thread execution logic including an
array of processing elements;
[0011] FIG. 6 is a block diagram of thread execution logic
including an array of processing elements;
[0012] FIG. 7 illustrates a graphics processor execution unit
instruction format according to an embodiment;
[0013] FIG. 8 is a block diagram of another embodiment of a
graphics processor which includes a graphics pipeline, a media
pipeline, a display engine, thread execution logic, and a render
output pipeline;
[0014] FIG. 9A is a block diagram illustrating a graphics processor
command format according to an embodiment;
[0015] FIG. 9B is a block diagram illustrating a graphics processor
command sequence according to an embodiment;
[0016] FIG. 10 illustrates exemplary graphics software architecture
for a data processing system according to an embodiment;
[0017] FIG. 11A illustrates exemplary IP core development systems
that may be used to manufacture an integrated circuit to perform
operations according to an embodiment;
[0018] FIGS. 11B-D illustrate exemplary packaging arrangements
including chiplets and interposer substrates;
[0019] FIG. 12 illustrates an exemplary system on a chip integrated
circuit that may be fabricated using one or more IP cores,
according to an embodiment;
[0020] FIG. 13 illustrates an exemplary graphics processor of a
system on a chip integrated circuit that may be fabricated using
one or more IP cores;
[0021] FIG. 14 illustrates an additional exemplary graphics
processor of a system on a chip integrated circuit that may be
fabricated using one or more IP cores;
[0022] FIG. 15 illustrates an architecture for performing initial
training of a machine-learning architecture;
[0023] FIG. 16 illustrates how a machine-learning engine is
continually trained and updated during runtime;
[0024] FIG. 17 illustrates how a machine-learning engine is
continually trained and updated during runtime;
[0025] FIGS. 18A-B illustrate how machine learning data is shared
on a network; and
[0026] FIG. 19 illustrates a method for training a machine-learning
engine;
[0027] FIG. 20 illustrates how nodes exchange ghost region data to
perform distributed denoising operations;
[0028] FIG. 21 illustrates an architecture in which image rendering
and denoising operations are distributed across a plurality of
nodes;
[0029] FIG. 22 illustrates additional details of an architecture
for distributed rendering and denoising;
[0030] FIG. 23 illustrates a method for performing distributed
rendering and denoising;
[0031] FIG. 24 illustrates a machine learning method;
[0032] FIG. 25 illustrates a plurality of interconnected general
purpose graphics processors;
[0033] FIG. 26 illustrates a set of convolutional layers and fully
connected layers for a machine learning implementation;
[0034] FIG. 27 illustrates an example of a convolutional layer;
[0035] FIG. 28 illustrates an example of a set of interconnected
nodes in a machine learning implementation;
[0036] FIG. 29 illustrates a training framework within which a
neural network learns using a training dataset;
[0037] FIG. 30A illustrates examples of model parallelism and data
parallelism;
[0038] FIG. 30B illustrates a system on a chip (SoC);
[0039] FIG. 31 illustrates a processing architecture which includes
ray tracing cores and tensor cores;
[0040] FIG. 32 illustrates an example of a beam;
[0041] FIG. 33 illustrates an apparatus for performing beam
tracing;
[0042] FIG. 34 illustrates an example of a beam hierarchy;
[0043] FIG. 35 illustrates a method for performing beam
tracing;
[0044] FIG. 36 illustrates an example of a distributed ray tracing
engine;
[0045] FIGS. 37-38 illustrate compression performed in a ray
tracing system;
[0046] FIG. 39 illustrates a method implemented on a ray tracing
architecture;
[0047] FIG. 40 illustrates an exemplary hybrid ray tracing
apparatus;
[0048] FIG. 41 illustrates stacks used for ray tracing
operations;
[0049] FIG. 42 illustrates additional details for a hybrid ray
tracing apparatus;
[0050] FIG. 43 illustrates a bounding volume hierarchy;
[0051] FIG. 44 illustrates a call stack and traversal state
storage;
[0052] FIG. 45 illustrates a method for traversal and
intersection;
[0053] FIGS. 46A-B illustrate how multiple dispatch cycles are
required to execute certain shaders;
[0054] FIG. 47 illustrates how a single dispatch cycle executes a
plurality of shaders;
[0055] FIG. 48 illustrates how a single dispatch cycle executes a
plurality of shaders;
[0056] FIG. 49 illustrates an architecture for executing ray
tracing instructions;
[0057] FIG. 50 illustrates a method for executing ray tracing
instructions within a thread;
[0058] FIG. 51 illustrates one embodiment of an architecture for
asynchronous ray tracing;
[0059] FIG. 52A illustrates one embodiment of a ray traversal
circuit;
[0060] FIG. 52B illustrates processes executed in one embodiment to
manage ray storage banks;
[0061] FIG. 53 illustrates one embodiment of priority selection
circuitry/logic;
[0062] FIGS. 54 and 55A-B illustrate different types of ray tracing
data including flags, exceptions, and culling data used in one
embodiment of the invention;
[0063] FIG. 56 illustrates one embodiment for determining early out
of the ray tracing pipeline;
[0064] FIG. 57 illustrates one embodiment of priority selection
circuitry/logic;
[0065] FIG. 58 illustrates an example bounding volume hierarchy
(BVH) used for ray traversal operations;
[0066] FIGS. 59A-B illustrate additional traversal operations;
[0067] FIG. 60 illustrates one embodiment of stack management
circuitry for managing a BVH stack;
[0068] FIGS. 61A-B illustrate example data structures,
sub-structures, and operations performed for rays, hits, and
stacks;
[0069] FIG. 62 illustrates an embodiment of a level of detail
selector with an N-bit comparison operation mask;
[0070] FIG. 63 illustrates an acceleration data structure in
accordance with one embodiment of the invention;
[0071] FIG. 64 illustrates one embodiment of a compression block
including residual values and metadata;
[0072] FIG. 65 illustrates a method in accordance with one
embodiment of the invention;
[0073] FIG. 66 illustrates one embodiment of a block offset index
compression block;
[0074] FIG. 67A illustrates a Hierarchical Bit-Vector Indexing
(HBI) in accordance with one embodiment of the invention;
[0075] FIG. 67B illustrates an index compression block in
accordance with one embodiment of the invention; and
[0076] FIG. 68 illustrates an example architecture including BVH
compression circuitry/logic and decompression circuitry/logic.
[0077] FIG. 69A illustrates a displacement function applied to a
mesh;
[0078] FIG. 69B illustrates one embodiment of compression circuitry
for compressing a mesh or meshlet;
[0079] FIG. 70A illustrates displacement mapping on a base
subdivision surface;
[0080] FIGS. 70B-C illustrates difference vectors relative to a
coarse base mesh;
[0081] FIG. 71 illustrates a method in accordance with one
embodiment of the invention;
[0082] FIGS. 72-74 illustrate a mesh comprising a plurality of
interconnected vertices;
[0083] FIG. 75 illustrates one embodiment of a tesselator for
generating a mesh;
[0084] FIGS. 76-77 illustrates one embodiment in which bounding
volumes are formed based on a mesh;
[0085] FIG. 78 illustrates one embodiment of a mesh sharing
overlapping vertices;
[0086] FIG. 79 illustrates a mesh with shared edges between
triangles;
[0087] FIG. 80 illustrates a ray tracing engine in accordance with
one embodiment;
[0088] FIG. 81 illustrate a BVH compressor in accordance with one
embodiment;
[0089] FIGS. 82A-C illustrate example data formats for a 64-bit
register;
[0090] FIGS. 83A-B illustrate one embodiment of an index for a ring
buffer;
[0091] FIG. 84A-B illustrate example ring buffer atomics for
producers and consumers;
[0092] FIG. 85A illustrates one embodiment of a tiled resource;
[0093] FIG. 85B illustrates a method in accordance with one
embodiment of the invention;
[0094] FIG. 86A illustrates one embodiment of BVH processing logic
including an on-demand builder;
[0095] FIG. 86B illustrates one embodiment of an on-demand builder
for an acceleration structure;
[0096] FIG. 86C illustrates one embodiment of a visible bottom
level acceleration structure map;
[0097] FIG. 86D illustrates different types of instances and
traversal decisions;
[0098] FIG. 87 illustrates one embodiment of a material-based cull
mask;
[0099] FIG. 88 illustrates one embodiment in which a quadtree
structure is formed over a geometry mesh;
[0100] FIG. 89A illustrates one embodiment of a ray tracing
architecture;
[0101] FIG. 89B illustrates one embodiment which includes meshlet
compression;
[0102] FIG. 90 illustrates a plurality of threads including
synchronous threads, diverging spawn threads, regular spawn
threads, and converging spawn threads;
[0103] FIG. 91 illustrates one embodiment of a ray tracing
architecture with a bindless thread dispatcher;
[0104] FIG. 92 illustrates a ray tracing cluster in accordance with
one embodiment;
[0105] FIG. 93-100 illustrate embodiments of using proxy data in a
multi-node ray tracing implementation;
[0106] FIG. 101 illustrates a method in accordance with one
embodiment of the invention.
DETAILED DESCRIPTION
[0107] In the following description, for the purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of the embodiments of the
invention described below. It will be apparent, however, to one
skilled in the art that the embodiments of the invention may be
practiced without some of these specific details. In other
instances, well-known structures and devices are shown in block
diagram form to avoid obscuring the underlying principles of the
embodiments of the invention.
Exemplary Graphics Processor Architectures and Data Types
System Overview
[0108] FIG. 1 is a block diagram of a processing system 100,
according to an embodiment. System 100 may be used in a single
processor desktop system, a multiprocessor workstation system, or a
server system having a large number of processors 102 or processor
cores 107. In one embodiment, the system 100 is a processing
platform incorporated within a system-on-a-chip (SoC) integrated
circuit for use in mobile, handheld, or embedded devices such as
within Internet-of-things (IoT) devices with wired or wireless
connectivity to a local or wide area network.
[0109] In one embodiment, system 100 can include, couple with, or
be integrated within: a server-based gaming platform; a game
console, including a game and media console; a mobile gaming
console, a handheld game console, or an online game console. In
some embodiments the system 100 is part of a mobile phone, smart
phone, tablet computing device or mobile Internet-connected device
such as a laptop with low internal storage capacity. Processing
system 100 can also include, couple with, or be integrated within:
a wearable device, such as a smart watch wearable device; smart
eyewear or clothing enhanced with augmented reality (AR) or virtual
reality (VR) features to provide visual, audio or tactile outputs
to supplement real world visual, audio or tactile experiences or
otherwise provide text, audio, graphics, video, holographic images
or video, or tactile feedback; other augmented reality (AR) device;
or other virtual reality (VR) device. In some embodiments, the
processing system 100 includes or is part of a television or set
top box device. In one embodiment, system 100 can include, couple
with, or be integrated within a self-driving vehicle such as a bus,
tractor trailer, car, motor or electric power cycle, plane or
glider (or any combination thereof). The self-driving vehicle may
use system 100 to process the environment sensed around the
vehicle.
[0110] In some embodiments, the one or more processors 102 each
include one or more processor cores 107 to process instructions
which, when executed, perform operations for system or user
software. In some embodiments, at least one of the one or more
processor cores 107 is configured to process a specific instruction
set 109. In some embodiments, instruction set 109 may facilitate
Complex Instruction Set Computing (CISC), Reduced Instruction Set
Computing (RISC), or computing via a Very Long Instruction Word
(VLIW). One or more processor cores 107 may process a different
instruction set 109, which may include instructions to facilitate
the emulation of other instruction sets. Processor core 107 may
also include other processing devices, such as a Digital Signal
Processor (DSP).
[0111] In some embodiments, the processor 102 includes cache memory
104. Depending on the architecture, the processor 102 can have a
single internal cache or multiple levels of internal cache. In some
embodiments, the cache memory is shared among various components of
the processor 102. In some embodiments, the processor 102 also uses
an external cache (e.g., a Level-3 (L3) cache or Last Level Cache
(LLC)) (not shown), which may be shared among processor cores 107
using known cache coherency techniques. A register file 106 can be
additionally included in processor 102 and may include different
types of registers for storing different types of data (e.g.,
integer registers, floating point registers, status registers, and
an instruction pointer register). Some registers may be
general-purpose registers, while other registers may be specific to
the design of the processor 102.
[0112] In some embodiments, one or more processor(s) 102 are
coupled with one or more interface bus(es) 110 to transmit
communication signals such as address, data, or control signals
between processor 102 and other components in the system 100. The
interface bus 110, in one embodiment, can be a processor bus, such
as a version of the Direct Media Interface (DMI) bus. However,
processor busses are not limited to the DMI bus, and may include
one or more Peripheral Component Interconnect buses (e.g., PCI, PCI
express), memory busses, or other types of interface busses. In one
embodiment the processor(s) 102 include an integrated memory
controller 116 and a platform controller hub 130. The memory
controller 116 facilitates communication between a memory device
and other components of the system 100, while the platform
controller hub (PCH) 130 provides connections to I/O devices via a
local I/O bus.
[0113] The memory device 120 can be a dynamic random-access memory
(DRAM) device, a static random-access memory (SRAM) device, flash
memory device, phase-change memory device, or some other memory
device having suitable performance to serve as process memory. In
one embodiment the memory device 120 can operate as system memory
for the system 100, to store data 122 and instructions 121 for use
when the one or more processors 102 executes an application or
process. Memory controller 116 also couples with an optional
external graphics processor 118, which may communicate with the one
or more graphics processors 108 in processors 102 to perform
graphics and media operations. In some embodiments, graphics,
media, and or compute operations may be assisted by an accelerator
112 which is a coprocessor that can be configured to perform a
specialized set of graphics, media, or compute operations. For
example, in one embodiment the accelerator 112 is a matrix
multiplication accelerator used to optimize machine learning or
compute operations. In one embodiment the accelerator 112 is a
ray-tracing accelerator that can be used to perform ray-tracing
operations in concert with the graphics processor 108. In one
embodiment, an external accelerator 119 may be used in place of or
in concert with the accelerator 112.
[0114] In some embodiments a display device 111 can connect to the
processor(s) 102. The display device 111 can be one or more of an
internal display device, as in a mobile electronic device or a
laptop device or an external display device attached via a display
interface (e.g., DisplayPort, etc.). In one embodiment the display
device 111 can be a head mounted display (HMD) such as a
stereoscopic display device for use in virtual reality (VR)
applications or augmented reality (AR) applications.
[0115] In some embodiments the platform controller hub 130 enables
peripherals to connect to memory device 120 and processor 102 via a
high-speed I/O bus. The I/O peripherals include, but are not
limited to, an audio controller 146, a network controller 134, a
firmware interface 128, a wireless transceiver 126, touch sensors
125, a data storage device 124 (e.g., non-volatile memory, volatile
memory, hard disk drive, flash memory, NAND, 3D NAND, 3D XPoint,
etc.). The data storage device 124 can connect via a storage
interface (e.g., SATA) or via a peripheral bus, such as a
Peripheral Component Interconnect bus (e.g., PCI, PCI express). The
touch sensors 125 can include touch screen sensors, pressure
sensors, or fingerprint sensors. The wireless transceiver 126 can
be a Wi-Fi transceiver, a Bluetooth transceiver, or a mobile
network transceiver such as a 3G, 4G, 5G, or Long-Term Evolution
(LTE) transceiver. The firmware interface 128 enables communication
with system firmware, and can be, for example, a unified extensible
firmware interface (UEFI). The network controller 134 can enable a
network connection to a wired network. In some embodiments, a
high-performance network controller (not shown) couples with the
interface bus 110. The audio controller 146, in one embodiment, is
a multi-channel high definition audio controller. In one embodiment
the system 100 includes an optional legacy I/O controller 140 for
coupling legacy (e.g., Personal System 2 (PS/2)) devices to the
system. The platform controller hub 130 can also connect to one or
more Universal Serial Bus (USB) controllers 142 connect input
devices, such as keyboard and mouse 143 combinations, a camera 144,
or other USB input devices.
[0116] It will be appreciated that the system 100 shown is
exemplary and not limiting, as other types of data processing
systems that are differently configured may also be used. For
example, an instance of the memory controller 116 and platform
controller hub 130 may be integrated into a discreet external
graphics processor, such as the external graphics processor 118. In
one embodiment the platform controller hub 130 and/or memory
controller 116 may be external to the one or more processor(s) 102.
For example, the system 100 can include an external memory
controller 116 and platform controller hub 130, which may be
configured as a memory controller hub and peripheral controller hub
within a system chipset that is in communication with the
processor(s) 102.
[0117] For example, circuit boards ("sleds") can be used on which
components such as CPUs, memory, and other components are placed
are designed for increased thermal performance. In some examples,
processing components such as the processors are located on a top
side of a sled while near memory, such as DIMMs, are located on a
bottom side of the sled. As a result of the enhanced airflow
provided by this design, the components may operate at higher
frequencies and power levels than in typical systems, thereby
increasing performance. Furthermore, the sleds are configured to
blindly mate with power and data communication cables in a rack,
thereby enhancing their ability to be quickly removed, upgraded,
reinstalled, and/or replaced. Similarly, individual components
located on the sleds, such as processors, accelerators, memory, and
data storage drives, are configured to be easily upgraded due to
their increased spacing from each other. In the illustrative
embodiment, the components additionally include hardware
attestation features to prove their authenticity.
[0118] A data center can utilize a single network architecture
("fabric") that supports multiple other network architectures
including Ethernet and Omni-Path. The sleds can be coupled to
switches via optical fibers, which provide higher bandwidth and
lower latency than typical twisted pair cabling (e.g., Category 5,
Category 5e, Category 6, etc.). Due to the high bandwidth, low
latency interconnections and network architecture, the data center
may, in use, pool resources, such as memory, accelerators (e.g.,
GPUs, graphics accelerators, FPGAs, ASICs, neural network and/or
artificial intelligence accelerators, etc.), and data storage
drives that are physically disaggregated, and provide them to
compute resources (e.g., processors) on an as needed basis,
enabling the compute resources to access the pooled resources as if
they were local.
[0119] A power supply or source can provide voltage and/or current
to system 100 or any component or system described herein. In one
example, the power supply includes an AC to DC (alternating current
to direct current) adapter to plug into a wall outlet. Such AC
power can be renewable energy (e.g., solar power) power source. In
one example, power source includes a DC power source, such as an
external AC to DC converter. In one example, power source or power
supply includes wireless charging hardware to charge via proximity
to a charging field. In one example, power source can include an
internal battery, alternating current supply, motion-based power
supply, solar power supply, or fuel cell source.
[0120] FIGS. 2A-2D illustrate computing systems and graphics
processors provided by embodiments described herein. The elements
of FIGS. 2A-2D having the same reference numbers (or names) as the
elements of any other figure herein can operate or function in any
manner similar to that described elsewhere herein, but are not
limited to such.
[0121] FIG. 2A is a block diagram of an embodiment of a processor
200 having one or more processor cores 202A-202N, an integrated
memory controller 214, and an integrated graphics processor 208.
Processor 200 can include additional cores up to and including
additional core 202N represented by the dashed lined boxes. Each of
processor cores 202A-202N includes one or more internal cache units
204A-204N. In some embodiments each processor core also has access
to one or more shared cached units 206. The internal cache units
204A-204N and shared cache units 206 represent a cache memory
hierarchy within the processor 200. The cache memory hierarchy may
include at least one level of instruction and data cache within
each processor core and one or more levels of shared mid-level
cache, such as a Level 2 (L2), Level 3 (L3), Level 4 (L4), or other
levels of cache, where the highest level of cache before external
memory is classified as the LLC. In some embodiments, cache
coherency logic maintains coherency between the various cache units
206 and 204A-204N.
[0122] In some embodiments, processor 200 may also include a set of
one or more bus controller units 216 and a system agent core 210.
The one or more bus controller units 216 manage a set of peripheral
buses, such as one or more PCI or PCI express busses. System agent
core 210 provides management functionality for the various
processor components. In some embodiments, system agent core 210
includes one or more integrated memory controllers 214 to manage
access to various external memory devices (not shown).
[0123] In some embodiments, one or more of the processor cores
202A-202N include support for simultaneous multi-threading. In such
embodiment, the system agent core 210 includes components for
coordinating and operating cores 202A-202N during multi-threaded
processing. System agent core 210 may additionally include a power
control unit (PCU), which includes logic and components to regulate
the power state of processor cores 202A-202N and graphics processor
208.
[0124] In some embodiments, processor 200 additionally includes
graphics processor 208 to execute graphics processing operations.
In some embodiments, the graphics processor 208 couples with the
set of shared cache units 206, and the system agent core 210,
including the one or more integrated memory controllers 214. In
some embodiments, the system agent core 210 also includes a display
controller 211 to drive graphics processor output to one or more
coupled displays. In some embodiments, display controller 211 may
also be a separate module coupled with the graphics processor via
at least one interconnect, or may be integrated within the graphics
processor 208.
[0125] In some embodiments, a ring-based interconnect unit 212 is
used to couple the internal components of the processor 200.
However, an alternative interconnect unit may be used, such as a
point-to-point interconnect, a switched interconnect, or other
techniques, including techniques well known in the art. In some
embodiments, graphics processor 208 couples with the ring
interconnect 212 via an I/O link 213.
[0126] The exemplary I/O link 213 represents at least one of
multiple varieties of I/O interconnects, including an on package
I/O interconnect which facilitates communication between various
processor components and a high-performance embedded memory module
218, such as an eDRAM module. In some embodiments, each of the
processor cores 202A-202N and graphics processor 208 can use
embedded memory modules 218 as a shared Last Level Cache.
[0127] In some embodiments, processor cores 202A-202N are
homogenous cores executing the same instruction set architecture.
In another embodiment, processor cores 202A-202N are heterogeneous
in terms of instruction set architecture (ISA), where one or more
of processor cores 202A-202N execute a first instruction set, while
at least one of the other cores executes a subset of the first
instruction set or a different instruction set. In one embodiment,
processor cores 202A-202N are heterogeneous in terms of
microarchitecture, where one or more cores having a relatively
higher power consumption couple with one or more power cores having
a lower power consumption. In one embodiment, processor cores
202A-202N are heterogeneous in terms of computational capability.
Additionally, processor 200 can be implemented on one or more chips
or as an SoC integrated circuit having the illustrated components,
in addition to other components.
[0128] FIG. 2B is a block diagram of hardware logic of a graphics
processor core 219, according to some embodiments described herein.
Elements of FIG. 2B having the same reference numbers (or names) as
the elements of any other figure herein can operate or function in
any manner similar to that described elsewhere herein, but are not
limited to such. The graphics processor core 219, sometimes
referred to as a core slice, can be one or multiple graphics cores
within a modular graphics processor. The graphics processor core
219 is exemplary of one graphics core slice, and a graphics
processor as described herein may include multiple graphics core
slices based on target power and performance envelopes. Each
graphics processor core 219 can include a fixed function block 230
coupled with multiple sub-cores 221A-221F, also referred to as
sub-slices, that include modular blocks of general-purpose and
fixed function logic.
[0129] In some embodiments, the fixed function block 230 includes a
geometry/fixed function pipeline 231 that can be shared by all
sub-cores in the graphics processor core 219, for example, in lower
performance and/or lower power graphics processor implementations.
In various embodiments, the geometry/fixed function pipeline 231
includes a 3D fixed function pipeline (e.g., 3D pipeline 312 as in
FIG. 3 and FIG. 4, described below) a video front-end unit, a
thread spawner and thread dispatcher, and a unified return buffer
manager, which manages unified return buffers (e.g., unified return
buffer 418 in FIG. 4, as described below).
[0130] In one embodiment the fixed function block 230 also includes
a graphics SoC interface 232, a graphics microcontroller 233, and a
media pipeline 234. The graphics SoC interface 232 provides an
interface between the graphics processor core 219 and other
processor cores within a system on a chip integrated circuit. The
graphics microcontroller 233 is a programmable sub-processor that
is configurable to manage various functions of the graphics
processor core 219, including thread dispatch, scheduling, and
pre-emption. The media pipeline 234 (e.g., media pipeline 316 of
FIG. 3 and FIG. 4) includes logic to facilitate the decoding,
encoding, pre-processing, and/or post-processing of multimedia
data, including image and video data. The media pipeline 234
implement media operations via requests to compute or sampling
logic within the sub-cores 221-221F.
[0131] In one embodiment the SoC interface 232 enables the graphics
processor core 219 to communicate with general-purpose application
processor cores (e.g., CPUs) and/or other components within an SoC,
including memory hierarchy elements such as a shared last level
cache memory, the system RAM, and/or embedded on-chip or on-package
DRAM. The SoC interface 232 can also enable communication with
fixed function devices within the SoC, such as camera imaging
pipelines, and enables the use of and/or implements global memory
atomics that may be shared between the graphics processor core 219
and CPUs within the SoC. The SoC interface 232 can also implement
power management controls for the graphics processor core 219 and
enable an interface between a clock domain of the graphic core 219
and other clock domains within the SoC. In one embodiment the SoC
interface 232 enables receipt of command buffers from a command
streamer and global thread dispatcher that are configured to
provide commands and instructions to each of one or more graphics
cores within a graphics processor. The commands and instructions
can be dispatched to the media pipeline 234, when media operations
are to be performed, or a geometry and fixed function pipeline
(e.g., geometry and fixed function pipeline 231, geometry and fixed
function pipeline 237) when graphics processing operations are to
be performed.
[0132] The graphics microcontroller 233 can be configured to
perform various scheduling and management tasks for the graphics
processor core 219. In one embodiment the graphics microcontroller
233 can perform graphics and/or compute workload scheduling on the
various graphics parallel engines within execution unit (EU) arrays
222A-222F, 224A-224F within the sub-cores 221A-221F. In this
scheduling model, host software executing on a CPU core of an SoC
including the graphics processor core 219 can submit workloads one
of multiple graphic processor doorbells, which invokes a scheduling
operation on the appropriate graphics engine. Scheduling operations
include determining which workload to run next, submitting a
workload to a command streamer, pre-empting existing workloads
running on an engine, monitoring progress of a workload, and
notifying host software when a workload is complete. In one
embodiment the graphics microcontroller 233 can also facilitate
low-power or idle states for the graphics processor core 219,
providing the graphics processor core 219 with the ability to save
and restore registers within the graphics processor core 219 across
low-power state transitions independently from the operating system
and/or graphics driver software on the system.
[0133] The graphics processor core 219 may have greater than or
fewer than the illustrated sub-cores 221A-221F, up to N modular
sub-cores. For each set of N sub-cores, the graphics processor core
219 can also include shared function logic 235, shared and/or cache
memory 236, a geometry/fixed function pipeline 237, as well as
additional fixed function logic 238 to accelerate various graphics
and compute processing operations. The shared function logic 235
can include logic units associated with the shared function logic
420 of FIG. 4 (e.g., sampler, math, and/or inter-thread
communication logic) that can be shared by each N sub-cores within
the graphics processor core 219. The shared and/or cache memory 236
can be a last-level cache for the set of N sub-cores 221A-221F
within the graphics processor core 219, and can also serve as
shared memory that is accessible by multiple sub-cores. The
geometry/fixed function pipeline 237 can be included instead of the
geometry/fixed function pipeline 231 within the fixed function
block 230 and can include the same or similar logic units.
[0134] In one embodiment the graphics processor core 219 includes
additional fixed function logic 238 that can include various fixed
function acceleration logic for use by the graphics processor core
219. In one embodiment the additional fixed function logic 238
includes an additional geometry pipeline for use in position only
shading. In position-only shading, two geometry pipelines exist,
the full geometry pipeline within the geometry/fixed function
pipeline 238, 231, and a cull pipeline, which is an additional
geometry pipeline which may be included within the additional fixed
function logic 238. In one embodiment the cull pipeline is a
trimmed down version of the full geometry pipeline. The full
pipeline and the cull pipeline can execute different instances of
the same application, each instance having a separate context.
Position only shading can hide long cull runs of discarded
triangles, enabling shading to be completed earlier in some
instances. For example and in one embodiment the cull pipeline
logic within the additional fixed function logic 238 can execute
position shaders in parallel with the main application and
generally generates critical results faster than the full pipeline,
as the cull pipeline fetches and shades only the position attribute
of the vertices, without performing rasterization and rendering of
the pixels to the frame buffer. The cull pipeline can use the
generated critical results to compute visibility information for
all the triangles without regard to whether those triangles are
culled. The full pipeline (which in this instance may be referred
to as a replay pipeline) can consume the visibility information to
skip the culled triangles to shade only the visible triangles that
are finally passed to the rasterization phase.
[0135] In one embodiment the additional fixed function logic 238
can also include machine-learning acceleration logic, such as fixed
function matrix multiplication logic, for implementations including
optimizations for machine learning training or inferencing.
[0136] Within each graphics sub-core 221A-221F includes a set of
execution resources that may be used to perform graphics, media,
and compute operations in response to requests by graphics
pipeline, media pipeline, or shader programs. The graphics
sub-cores 221A-221F include multiple EU arrays 222A-222F,
224A-224F, thread dispatch and inter-thread communication (TD/IC)
logic 223A-223F, a 3D (e.g., texture) sampler 225A-225F, a media
sampler 206A-206F, a shader processor 227A-227F, and shared local
memory (SLM) 228A-228F. The EU arrays 222A-222F, 224A-224F each
include multiple execution units, which are general-purpose
graphics processing units capable of performing floating-point and
integer/fixed-point logic operations in service of a graphics,
media, or compute operation, including graphics, media, or compute
shader programs. The TD/IC logic 223A-223F performs local thread
dispatch and thread control operations for the execution units
within a sub-core and facilitate communication between threads
executing on the execution units of the sub-core. The 3D sampler
225A-225F can read texture or other 3D graphics related data into
memory. The 3D sampler can read texture data differently based on a
configured sample state and the texture format associated with a
given texture. The media sampler 206A-206F can perform similar read
operations based on the type and format associated with media data.
In one embodiment, each graphics sub-core 221A-221F can alternately
include a unified 3D and media sampler. Threads executing on the
execution units within each of the sub-cores 221A-221F can make use
of shared local memory 228A-228F within each sub-core, to enable
threads executing within a thread group to execute using a common
pool of on-chip memory.
[0137] FIG. 2C illustrates a graphics processing unit (GPU) 239
that includes dedicated sets of graphics processing resources
arranged into multi-core groups 240A-240N. While the details of
only a single multi-core group 240A are provided, it will be
appreciated that the other multi-core groups 240B-240N may be
equipped with the same or similar sets of graphics processing
resources.
[0138] As illustrated, a multi-core group 240A may include a set of
graphics cores 243, a set of tensor cores 244, and a set of ray
tracing cores 245. A scheduler/dispatcher 241 schedules and
dispatches the graphics threads for execution on the various cores
243, 244, 245. A set of register files 242 store operand values
used by the cores 243, 244, 245 when executing the graphics
threads. These may include, for example, integer registers for
storing integer values, floating point registers for storing
floating point values, vector registers for storing packed data
elements (integer and/or floating point data elements) and tile
registers for storing tensor/matrix values. In one embodiment, the
tile registers are implemented as combined sets of vector
registers.
[0139] One or more combined level 1 (L1) caches and shared memory
units 247 store graphics data such as texture data, vertex data,
pixel data, ray data, bounding volume data, etc., locally within
each multi-core group 240A. One or more texture units 247 can also
be used to perform texturing operations, such as texture mapping
and sampling. A Level 2 (L2) cache 253 shared by all or a subset of
the multi-core groups 240A-240N stores graphics data and/or
instructions for multiple concurrent graphics threads. As
illustrated, the L2 cache 253 may be shared across a plurality of
multi-core groups 240A-240N. One or more memory controllers 248
couple the GPU 239 to a memory 249 which may be a system memory
(e.g., DRAM) and/or a dedicated graphics memory (e.g., GDDR6
memory).
[0140] Input/output (I/O) circuitry 250 couples the GPU 239 to one
or more I/O devices 252 such as digital signal processors (DSPs),
network controllers, or user input devices. An on-chip interconnect
may be used to couple the I/O devices 252 to the GPU 239 and memory
249. One or more I/O memory management units (IOMMUs) 251 of the
I/O circuitry 250 couple the I/O devices 252 directly to the system
memory 249. In one embodiment, the IOMMU 251 manages multiple sets
of page tables to map virtual addresses to physical addresses in
system memory 249. In this embodiment, the I/O devices 252, CPU(s)
246, and GPU(s) 239 may share the same virtual address space.
[0141] In one implementation, the IOMMU 251 supports
virtualization. In this case, it may manage a first set of page
tables to map guest/graphics virtual addresses to guest/graphics
physical addresses and a second set of page tables to map the
guest/graphics physical addresses to system/host physical addresses
(e.g., within system memory 249). The base addresses of each of the
first and second sets of page tables may be stored in control
registers and swapped out on a context switch (e.g., so that the
new context is provided with access to the relevant set of page
tables). While not illustrated in FIG. 2C, each of the cores 243,
244, 245 and/or multi-core groups 240A-240N may include translation
lookaside buffers (TLBs) to cache guest virtual to guest physical
translations, guest physical to host physical translations, and
guest virtual to host physical translations.
[0142] In one embodiment, the CPUs 246, GPUs 239, and I/O devices
252 are integrated on a single semiconductor chip and/or chip
package. The illustrated memory 249 may be integrated on the same
chip or may be coupled to the memory controllers 248 via an
off-chip interface. In one implementation, the memory 249 comprises
GDDR6 memory which shares the same virtual address space as other
physical system-level memories, although the underlying principles
of the invention are not limited to this specific
implementation.
[0143] In one embodiment, the tensor cores 244 include a plurality
of execution units specifically designed to perform matrix
operations, which are the fundamental compute operation used to
perform deep learning operations. For example, simultaneous matrix
multiplication operations may be used for neural network training
and inferencing. The tensor cores 244 may perform matrix processing
using a variety of operand precisions including single precision
floating-point (e.g., 32 bits), half-precision floating point
(e.g., 16 bits), integer words (16 bits), bytes (8 bits), and
half-bytes (4 bits). In one embodiment, a neural network
implementation extracts features of each rendered scene,
potentially combining details from multiple frames, to construct a
high-quality final image.
[0144] In deep learning implementations, parallel matrix
multiplication work may be scheduled for execution on the tensor
cores 244. The training of neural networks, in particular, requires
a significant number matrix dot product operations. In order to
process an inner-product formulation of an N.times.N.times.N matrix
multiply, the tensor cores 244 may include at least N dot-product
processing elements. Before the matrix multiply begins, one entire
matrix is loaded into tile registers and at least one column of a
second matrix is loaded each cycle for N cycles. Each cycle, there
are N dot products that are processed.
[0145] Matrix elements may be stored at different precisions
depending on the particular implementation, including 16-bit words,
8-bit bytes (e.g., INT8) and 4-bit half-bytes (e.g., INT4).
Different precision modes may be specified for the tensor cores 244
to ensure that the most efficient precision is used for different
workloads (e.g., such as inferencing workloads which can tolerate
quantization to bytes and half-bytes).
[0146] In one embodiment, the ray tracing cores 245 accelerate ray
tracing operations for both real-time ray tracing and non-real-time
ray tracing implementations. In particular, the ray tracing cores
245 include ray traversal/intersection circuitry for performing ray
traversal using bounding volume hierarchies (BVHs) and identifying
intersections between rays and primitives enclosed within the BVH
volumes. The ray tracing cores 245 may also include circuitry for
performing depth testing and culling (e.g., using a Z buffer or
similar arrangement). In one implementation, the ray tracing cores
245 perform traversal and intersection operations in concert with
the image denoising techniques described herein, at least a portion
of which may be executed on the tensor cores 244. For example, in
one embodiment, the tensor cores 244 implement a deep learning
neural network to perform comprising a local memory 9010 (and/or
system memory) denoising of frames generated by the ray tracing
cores 245. However, the CPU(s) 246, graphics cores 243, and/or ray
tracing cores 245 may also implement all or a portion of the
denoising and/or deep learning algorithms.
[0147] In addition, as described above, a distributed approach to
denoising may be employed in which the GPU 239 is in a computing
device coupled to other computing devices over a network or high
speed interconnect. In this embodiment, the interconnected
computing devices share neural network learning/training data to
improve the speed with which the overall system learns to perform
denoising for different types of image frames and/or different
graphics applications.
[0148] In one embodiment, the ray tracing cores 245 process all BVH
traversal and ray-primitive intersections, saving the graphics
cores 243 from being overloaded with thousands of instructions per
ray. In one embodiment, each ray tracing core 245 includes a first
set of specialized circuitry for performing bounding box tests
(e.g., for traversal operations) and a second set of specialized
circuitry for performing the ray-triangle intersection tests (e.g.,
intersecting rays which have been traversed). Thus, in one
embodiment, the multi-core group 240A can simply launch a ray
probe, and the ray tracing cores 245 independently perform ray
traversal and intersection and return hit data (e.g., a hit, no
hit, multiple hits, etc.) to the thread context. The other cores
243, 244 are freed to perform other graphics or compute work while
the ray tracing cores 245 perform the traversal and intersection
operations.
[0149] In one embodiment, each ray tracing core 245 includes a
traversal unit to perform BVH testing operations and an
intersection unit which performs ray-primitive intersection tests.
The intersection unit generates a "hit", "no hit", or "multiple
hit" response, which it provides to the appropriate thread. During
the traversal and intersection operations, the execution resources
of the other cores (e.g., graphics cores 243 and tensor cores 244)
are freed to perform other forms of graphics work.
[0150] In one particular embodiment described below, a hybrid
rasterization/ray tracing approach is used in which work is
distributed between the graphics cores 243 and ray tracing cores
245.
[0151] In one embodiment, the ray tracing cores 245 (and/or other
cores 243, 244) include hardware support for a ray tracing
instruction set such as Microsoft's DirectX Ray Tracing (DXR) which
includes a DispatchRays command, as well as ray-generation,
closest-hit, any-hit, and miss shaders, which enable the assignment
of unique sets of shaders and textures for each object. Another ray
tracing platform which may be supported by the ray tracing cores
245, graphics cores 243 and tensor cores 244 is Vulkan 1.1.85.
Note, however, that the underlying principles of the invention are
not limited to any particular ray tracing ISA.
[0152] In general, the various cores 245, 244, 243 may support a
ray tracing instruction set that includes instructions/functions
for ray generation, closest hit, any hit, ray-primitive
intersection, per-primitive and hierarchical bounding box
construction, miss, visit, and exceptions. More specifically, one
embodiment includes ray tracing instructions to perform the
following functions:
[0153] Ray Generation--Ray generation instructions may be executed
for each pixel, sample, or other user-defined work assignment.
[0154] Closest Hit--A closest hit instruction may be executed to
locate the closest intersection point of a ray with primitives
within a scene.
[0155] Any Hit--An any hit instruction identifies multiple
intersections between a ray and primitives within a scene,
potentially to identify a new closest intersection point.
[0156] Intersection--An intersection instruction performs a
ray-primitive intersection test and outputs a result.
[0157] Per-primitive Bounding box Construction--This instruction
builds a bounding box around a given primitive or group of
primitives (e.g., when building a new BVH or other acceleration
data structure).
[0158] Miss--Indicates that a ray misses all geometry within a
scene, or specified region of a scene.
[0159] Visit--Indicates the children volumes a ray will
traverse.
[0160] Exceptions--Includes various types of exception handlers
(e.g., invoked for various error conditions).
[0161] FIG. 2D is a block diagram of general purpose graphics
processing unit (GPGPU) 270 that can be configured as a graphics
processor and/or compute accelerator, according to embodiments
described herein. The GPGPU 270 can interconnect with host
processors (e.g., one or more CPU(s) 246) and memory 271, 272 via
one or more system and/or memory busses. In one embodiment the
memory 271 is system memory that may be shared with the one or more
CPU(s) 246, while memory 272 is device memory that is dedicated to
the GPGPU 270. In one embodiment, components within the GPGPU 270
and device memory 272 may be mapped into memory addresses that are
accessible to the one or more CPU(s) 246. Access to memory 271 and
272 may be facilitated via a memory controller 268. In one
embodiment the memory controller 268 includes an internal direct
memory access (DMA) controller 269 or can include logic to perform
operations that would otherwise be performed by a DMA
controller.
[0162] The GPGPU 270 includes multiple cache memories, including an
L2 cache 253, L1 cache 254, an instruction cache 255, and shared
memory 256, at least a portion of which may also be partitioned as
a cache memory. The GPGPU 270 also includes multiple compute units
260A-260N. Each compute unit 260A-260N includes a set of vector
registers 261, scalar registers 262, vector logic units 263, and
scalar logic units 264. The compute units 260A-260N can also
include local shared memory 265 and a program counter 266. The
compute units 260A-260N can couple with a constant cache 267, which
can be used to store constant data, which is data that will not
change during the run of kernel or shader program that executes on
the GPGPU 270. In one embodiment the constant cache 267 is a scalar
data cache and cached data can be fetched directly into the scalar
registers 262.
[0163] During operation, the one or more CPU(s) 246 can write
commands into registers or memory in the GPGPU 270 that has been
mapped into an accessible address space. The command processors 257
can read the commands from registers or memory and determine how
those commands will be processed within the GPGPU 270. A thread
dispatcher 258 can then be used to dispatch threads to the compute
units 260A-260N to perform those commands. Each compute unit
260A-260N can execute threads independently of the other compute
units. Additionally each compute unit 260A-260N can be
independently configured for conditional computation and can
conditionally output the results of computation to memory. The
command processors 257 can interrupt the one or more CPU(s) 246
when the submitted commands are complete.
[0164] FIGS. 3A-3C illustrate block diagrams of additional graphics
processor and compute accelerator architectures provided by
embodiments described herein. The elements of FIGS. 3A-3C having
the same reference numbers (or names) as the elements of any other
figure herein can operate or function in any manner similar to that
described elsewhere herein, but are not limited to such.
[0165] FIG. 3A is a block diagram of a graphics processor 300,
which may be a discrete graphics processing unit, or may be a
graphics processor integrated with a plurality of processing cores,
or other semiconductor devices such as, but not limited to, memory
devices or network interfaces. In some embodiments, the graphics
processor communicates via a memory mapped I/O interface to
registers on the graphics processor and with commands placed into
the processor memory. In some embodiments, graphics processor 300
includes a memory interface 314 to access memory. Memory interface
314 can be an interface to local memory, one or more internal
caches, one or more shared external caches, and/or to system
memory.
[0166] In some embodiments, graphics processor 300 also includes a
display controller 302 to drive display output data to a display
device 318. Display controller 302 includes hardware for one or
more overlay planes for the display and composition of multiple
layers of video or user interface elements. The display device 318
can be an internal or external display device. In one embodiment
the display device 318 is a head mounted display device, such as a
virtual reality (VR) display device or an augmented reality (AR)
display device. In some embodiments, graphics processor 300
includes a video codec engine 306 to encode, decode, or transcode
media to, from, or between one or more media encoding formats,
including, but not limited to Moving Picture Experts Group (MPEG)
formats such as MPEG-2, Advanced Video Coding (AVC) formats such as
H.264/MPEG-4 AVC, H.265/HEVC, Alliance for Open Media (AOMedia)
VP8, VP9, as well as the Society of Motion Picture & Television
Engineers (SMPTE) 421M/VC-1, and Joint Photographic Experts Group
(JPEG) formats such as JPEG, and Motion JPEG (MJPEG) formats.
[0167] In some embodiments, graphics processor 300 includes a block
image transfer (BLIT) engine 304 to perform two-dimensional (2D)
rasterizer operations including, for example, bit-boundary block
transfers. However, in one embodiment, 2D graphics operations are
performed using one or more components of graphics processing
engine (GPE) 310. In some embodiments, GPE 310 is a compute engine
for performing graphics operations, including three-dimensional
(3D) graphics operations and media operations.
[0168] In some embodiments, GPE 310 includes a 3D pipeline 312 for
performing 3D operations, such as rendering three-dimensional
images and scenes using processing functions that act upon 3D
primitive shapes (e.g., rectangle, triangle, etc.). The 3D pipeline
312 includes programmable and fixed function elements that perform
various tasks within the element and/or spawn execution threads to
a 3D/Media sub-system 315. While 3D pipeline 312 can be used to
perform media operations, an embodiment of GPE 310 also includes a
media pipeline 316 that is specifically used to perform media
operations, such as video post-processing and image
enhancement.
[0169] In some embodiments, media pipeline 316 includes fixed
function or programmable logic units to perform one or more
specialized media operations, such as video decode acceleration,
video de-interlacing, and video encode acceleration in place of, or
on behalf of video codec engine 306. In some embodiments, media
pipeline 316 additionally includes a thread spawning unit to spawn
threads for execution on 3D/Media sub-system 315. The spawned
threads perform computations for the media operations on one or
more graphics execution units included in 3D/Media sub-system
315.
[0170] In some embodiments, 3D/Media subsystem 315 includes logic
for executing threads spawned by 3D pipeline 312 and media pipeline
316. In one embodiment, the pipelines send thread execution
requests to 3D/Media subsystem 315, which includes thread dispatch
logic for arbitrating and dispatching the various requests to
available thread execution resources. The execution resources
include an array of graphics execution units to process the 3D and
media threads. In some embodiments, 3D/Media subsystem 315 includes
one or more internal caches for thread instructions and data. In
some embodiments, the subsystem also includes shared memory,
including registers and addressable memory, to share data between
threads and to store output data.
[0171] FIG. 3B illustrates a graphics processor 320 having a tiled
architecture, according to embodiments described herein. In one
embodiment the graphics processor 320 includes a graphics
processing engine cluster 322 having multiple instances of the
graphics processing engine 310 of FIG. 3A within a graphics engine
tile 310A-310D. Each graphics engine tile 310A-310D can be
interconnected via a set of tile interconnects 323A-323F. Each
graphics engine tile 310A-310D can also be connected to a memory
module or memory device 326A-326D via memory interconnects
325A-325D. The memory devices 326A-326D can use any graphics memory
technology. For example, the memory devices 326A-326D may be
graphics double data rate (GDDR) memory. The memory devices
326A-326D, in one embodiment, are high-bandwidth memory (HBM)
modules that can be on-die with their respective graphics engine
tile 310A-310D. In one embodiment the memory devices 326A-326D are
stacked memory devices that can be stacked on top of their
respective graphics engine tile 310A-310D. In one embodiment, each
graphics engine tile 310A-310D and associated memory 326A-326D
reside on separate chiplets, which are bonded to a base die or base
substrate, as described on further detail in FIGS. 11B-11D.
[0172] The graphics processing engine cluster 322 can connect with
an on-chip or on-package fabric interconnect 324. The fabric
interconnect 324 can enable communication between graphics engine
tiles 310A-310D and components such as the video codec 306 and one
or more copy engines 304. The copy engines 304 can be used to move
data out of, into, and between the memory devices 326A-326D and
memory that is external to the graphics processor 320 (e.g., system
memory). The fabric interconnect 324 can also be used to
interconnect the graphics engine tiles 310A-310D. The graphics
processor 320 may optionally include a display controller 302 to
enable a connection with an external display device 318. The
graphics processor may also be configured as a graphics or compute
accelerator. In the accelerator configuration, the display
controller 302 and display device 318 may be omitted.
[0173] The graphics processor 320 can connect to a host system via
a host interface 328. The host interface 328 can enable
communication between the graphics processor 320, system memory,
and/or other system components. The host interface 328 can be, for
example a PCI express bus or another type of host system
interface.
[0174] FIG. 3C illustrates a compute accelerator 330, according to
embodiments described herein. The compute accelerator 330 can
include architectural similarities with the graphics processor 320
of FIG. 3B and is optimized for compute acceleration. A compute
engine cluster 332 can include a set of compute engine tiles
340A-340D that include execution logic that is optimized for
parallel or vector-based general-purpose compute operations. In
some embodiments, the compute engine tiles 340A-340D do not include
fixed function graphics processing logic, although in one
embodiment one or more of the compute engine tiles 340A-340D can
include logic to perform media acceleration. The compute engine
tiles 340A-340D can connect to memory 326A-326D via memory
interconnects 325A-325D. The memory 326A-326D and memory
interconnects 325A-325D may be similar technology as in graphics
processor 320, or can be different. The graphics compute engine
tiles 340A-340D can also be interconnected via a set of tile
interconnects 323A-323F and may be connected with and/or
interconnected by a fabric interconnect 324. In one embodiment the
compute accelerator 330 includes a large L3 cache 336 that can be
configured as a device-wide cache. The compute accelerator 330 can
also connect to a host processor and memory via a host interface
328 in a similar manner as the graphics processor 320 of FIG.
3B.
[0175] Graphics Processing Engine
[0176] FIG. 4 is a block diagram of a graphics processing engine
410 of a graphics processor in accordance with some embodiments. In
one embodiment, the graphics processing engine (GPE) 410 is a
version of the GPE 310 shown in FIG. 3A, and may also represent a
graphics engine tile 310A-310D of FIG. 3B. Elements of FIG. 4
having the same reference numbers (or names) as the elements of any
other figure herein can operate or function in any manner similar
to that described elsewhere herein, but are not limited to such.
For example, the 3D pipeline 312 and media pipeline 316 of FIG. 3A
are illustrated. The media pipeline 316 is optional in some
embodiments of the GPE 410 and may not be explicitly included
within the GPE 410. For example and in at least one embodiment, a
separate media and/or image processor is coupled to the GPE
410.
[0177] In some embodiments, GPE 410 couples with or includes a
command streamer 403, which provides a command stream to the 3D
pipeline 312 and/or media pipelines 316. In some embodiments,
command streamer 403 is coupled with memory, which can be system
memory, or one or more of internal cache memory and shared cache
memory. In some embodiments, command streamer 403 receives commands
from the memory and sends the commands to 3D pipeline 312 and/or
media pipeline 316. The commands are directives fetched from a ring
buffer, which stores commands for the 3D pipeline 312 and media
pipeline 316. In one embodiment, the ring buffer can additionally
include batch command buffers storing batches of multiple commands.
The commands for the 3D pipeline 312 can also include references to
data stored in memory, such as but not limited to vertex and
geometry data for the 3D pipeline 312 and/or image data and memory
objects for the media pipeline 316. The 3D pipeline 312 and media
pipeline 316 process the commands and data by performing operations
via logic within the respective pipelines or by dispatching one or
more execution threads to a graphics core array 414. In one
embodiment the graphics core array 414 include one or more blocks
of graphics cores (e.g., graphics core(s) 415A, graphics core(s)
415B), each block including one or more graphics cores. Each
graphics core includes a set of graphics execution resources that
includes general-purpose and graphics specific execution logic to
perform graphics and compute operations, as well as fixed function
texture processing and/or machine learning and artificial
intelligence acceleration logic.
[0178] In various embodiments the 3D pipeline 312 can include fixed
function and programmable logic to process one or more shader
programs, such as vertex shaders, geometry shaders, pixel shaders,
fragment shaders, compute shaders, or other shader programs, by
processing the instructions and dispatching execution threads to
the graphics core array 414. The graphics core array 414 provides a
unified block of execution resources for use in processing these
shader programs. Multi-purpose execution logic (e.g., execution
units) within the graphics core(s) 415A-414B of the graphic core
array 414 includes support for various 3D API shader languages and
can execute multiple simultaneous execution threads associated with
multiple shaders.
[0179] In some embodiments, the graphics core array 414 includes
execution logic to perform media functions, such as video and/or
image processing. In one embodiment, the execution units include
general-purpose logic that is programmable to perform parallel
general-purpose computational operations, in addition to graphics
processing operations. The general-purpose logic can perform
processing operations in parallel or in conjunction with
general-purpose logic within the processor core(s) 107 of FIG. 1 or
core 202A-202N as in FIG. 2A.
[0180] Output data generated by threads executing on the graphics
core array 414 can output data to memory in a unified return buffer
(URB) 418. The URB 418 can store data for multiple threads. In some
embodiments the URB 418 may be used to send data between different
threads executing on the graphics core array 414. In some
embodiments the URB 418 may additionally be used for
synchronization between threads on the graphics core array and
fixed function logic within the shared function logic 420.
[0181] In some embodiments, graphics core array 414 is scalable,
such that the array includes a variable number of graphics cores,
each having a variable number of execution units based on the
target power and performance level of GPE 410. In one embodiment
the execution resources are dynamically scalable, such that
execution resources may be enabled or disabled as needed.
[0182] The graphics core array 414 couples with shared function
logic 420 that includes multiple resources that are shared between
the graphics cores in the graphics core array. The shared functions
within the shared function logic 420 are hardware logic units that
provide specialized supplemental functionality to the graphics core
array 414. In various embodiments, shared function logic 420
includes but is not limited to sampler 421, math 422, and
inter-thread communication (ITC) 423 logic. Additionally, some
embodiments implement one or more cache(s) 425 within the shared
function logic 420.
[0183] A shared function is implemented at least in a case where
the demand for a given specialized function is insufficient for
inclusion within the graphics core array 414. Instead a single
instantiation of that specialized function is implemented as a
stand-alone entity in the shared function logic 420 and shared
among the execution resources within the graphics core array 414.
The precise set of functions that are shared between the graphics
core array 414 and included within the graphics core array 414
varies across embodiments. In some embodiments, specific shared
functions within the shared function logic 420 that are used
extensively by the graphics core array 414 may be included within
shared function logic 416 within the graphics core array 414. In
various embodiments, the shared function logic 416 within the
graphics core array 414 can include some or all logic within the
shared function logic 420. In one embodiment, all logic elements
within the shared function logic 420 may be duplicated within the
shared function logic 416 of the graphics core array 414. In one
embodiment the shared function logic 420 is excluded in favor of
the shared function logic 416 within the graphics core array
414.
[0184] Execution Units
[0185] FIGS. 5A-5B illustrate thread execution logic 500 including
an array of processing elements employed in a graphics processor
core according to embodiments described herein. Elements of FIGS.
5A-5B having the same reference numbers (or names) as the elements
of any other figure herein can operate or function in any manner
similar to that described elsewhere herein, but are not limited to
such. FIG. 5A-5B illustrates an overview of thread execution logic
500, which may be representative of hardware logic illustrated with
each sub-core 221A-221F of FIG. 2B. FIG. 5A is representative of an
execution unit within a general-purpose graphics processor, while
FIG. 5B is representative of an execution unit that may be used
within a compute accelerator.
[0186] As illustrated in FIG. 5A, in some embodiments thread
execution logic 500 includes a shader processor 502, a thread
dispatcher 504, instruction cache 506, a scalable execution unit
array including a plurality of execution units 508A-508N, a sampler
510, shared local memory 511, a data cache 512, and a data port
514. In one embodiment the scalable execution unit array can
dynamically scale by enabling or disabling one or more execution
units (e.g., any of execution units 508A, 508B, 508C, 508D, through
508N-1 and 508N) based on the computational requirements of a
workload. In one embodiment the included components are
interconnected via an interconnect fabric that links to each of the
components. In some embodiments, thread execution logic 500
includes one or more connections to memory, such as system memory
or cache memory, through one or more of instruction cache 506, data
port 514, sampler 510, and execution units 508A-508N. In some
embodiments, each execution unit (e.g. 508A) is a stand-alone
programmable general-purpose computational unit that is capable of
executing multiple simultaneous hardware threads while processing
multiple data elements in parallel for each thread. In various
embodiments, the array of execution units 508A-508N is scalable to
include any number individual execution units.
[0187] In some embodiments, the execution units 508A-508N are
primarily used to execute shader programs. A shader processor 502
can process the various shader programs and dispatch execution
threads associated with the shader programs via a thread dispatcher
504. In one embodiment the thread dispatcher includes logic to
arbitrate thread initiation requests from the graphics and media
pipelines and instantiate the requested threads on one or more
execution unit in the execution units 508A-508N. For example, a
geometry pipeline can dispatch vertex, tessellation, or geometry
shaders to the thread execution logic for processing. In some
embodiments, thread dispatcher 504 can also process runtime thread
spawning requests from the executing shader programs.
[0188] In some embodiments, the execution units 508A-508N support
an instruction set that includes native support for many standard
3D graphics shader instructions, such that shader programs from
graphics libraries (e.g., Direct 3D and OpenGL) are executed with a
minimal translation. The execution units support vertex and
geometry processing (e.g., vertex programs, geometry programs,
vertex shaders), pixel processing (e.g., pixel shaders, fragment
shaders) and general-purpose processing (e.g., compute and media
shaders). Each of the execution units 508A-508N is capable of
multi-issue single instruction multiple data (SIMD) execution and
multi-threaded operation enables an efficient execution environment
in the face of higher latency memory accesses. Each hardware thread
within each execution unit has a dedicated high-bandwidth register
file and associated independent thread-state. Execution is
multi-issue per clock to pipelines capable of integer, single and
double precision floating point operations, SIMD branch capability,
logical operations, transcendental operations, and other
miscellaneous operations. While waiting for data from memory or one
of the shared functions, dependency logic within the execution
units 508A-508N causes a waiting thread to sleep until the
requested data has been returned. While the waiting thread is
sleeping, hardware resources may be devoted to processing other
threads. For example, during a delay associated with a vertex
shader operation, an execution unit can perform operations for a
pixel shader, fragment shader, or another type of shader program,
including a different vertex shader. Various embodiments can apply
to use execution by use of Single Instruction Multiple Thread
(SIMT) as an alternate to use of SIMD or in addition to use of
SIMD. Reference to a SIMD core or operation can apply also to SIMT
or apply to SIMD in combination with SIMT.
[0189] Each execution unit in execution units 508A-508N operates on
arrays of data elements. The number of data elements is the
"execution size," or the number of channels for the instruction. An
execution channel is a logical unit of execution for data element
access, masking, and flow control within instructions. The number
of channels may be independent of the number of physical Arithmetic
Logic Units (ALUs) or Floating Point Units (FPUs) for a particular
graphics processor. In some embodiments, execution units 508A-508N
support integer and floating-point data types.
[0190] The execution unit instruction set includes SIMD
instructions. The various data elements can be stored as a packed
data type in a register and the execution unit will process the
various elements based on the data size of the elements. For
example, when operating on a 256-bit wide vector, the 256 bits of
the vector are stored in a register and the execution unit operates
on the vector as four separate 54-bit packed data elements
(Quad-Word (QW) size data elements), eight separate 32-bit packed
data elements (Double Word (DW) size data elements), sixteen
separate 16-bit packed data elements (Word (W) size data elements),
or thirty-two separate 8-bit data elements (byte (B) size data
elements). However, different vector widths and register sizes are
possible.
[0191] In one embodiment one or more execution units can be
combined into a fused execution unit 509A-509N having thread
control logic (507A-507N) that is common to the fused EUs. Multiple
EUs can be fused into an EU group. Each EU in the fused EU group
can be configured to execute a separate SIMD hardware thread. The
number of EUs in a fused EU group can vary according to
embodiments. Additionally, various SIMD widths can be performed
per-EU, including but not limited to SIMD8, SIMD16, and SIMD32.
Each fused graphics execution unit 509A-509N includes at least two
execution units. For example, fused execution unit 509A includes a
first EU 508A, second EU 508B, and thread control logic 507A that
is common to the first EU 508A and the second EU 508B. The thread
control logic 507A controls threads executed on the fused graphics
execution unit 509A, allowing each EU within the fused execution
units 509A-509N to execute using a common instruction pointer
register.
[0192] One or more internal instruction caches (e.g., 506) are
included in the thread execution logic 500 to cache thread
instructions for the execution units. In some embodiments, one or
more data caches (e.g., 512) are included to cache thread data
during thread execution. Threads executing on the execution logic
500 can also store explicitly managed data in the shared local
memory 511. In some embodiments, a sampler 510 is included to
provide texture sampling for 3D operations and media sampling for
media operations. In some embodiments, sampler 510 includes
specialized texture or media sampling functionality to process
texture or media data during the sampling process before providing
the sampled data to an execution unit.
[0193] During execution, the graphics and media pipelines send
thread initiation requests to thread execution logic 500 via thread
spawning and dispatch logic. Once a group of geometric objects has
been processed and rasterized into pixel data, pixel processor
logic (e.g., pixel shader logic, fragment shader logic, etc.)
within the shader processor 502 is invoked to further compute
output information and cause results to be written to output
surfaces (e.g., color buffers, depth buffers, stencil buffers,
etc.). In some embodiments, a pixel shader or fragment shader
calculates the values of the various vertex attributes that are to
be interpolated across the rasterized object. In some embodiments,
pixel processor logic within the shader processor 502 then executes
an application programming interface (API)-supplied pixel or
fragment shader program. To execute the shader program, the shader
processor 502 dispatches threads to an execution unit (e.g., 508A)
via thread dispatcher 504. In some embodiments, shader processor
502 uses texture sampling logic in the sampler 510 to access
texture data in texture maps stored in memory. Arithmetic
operations on the texture data and the input geometry data compute
pixel color data for each geometric fragment, or discards one or
more pixels from further processing.
[0194] In some embodiments, the data port 514 provides a memory
access mechanism for the thread execution logic 500 to output
processed data to memory for further processing on a graphics
processor output pipeline. In some embodiments, the data port 514
includes or couples to one or more cache memories (e.g., data cache
512) to cache data for memory access via the data port.
[0195] In one embodiment, the execution logic 500 can also include
a ray tracer 505 that can provide ray tracing acceleration
functionality. The ray tracer 505 can support a ray tracing
instruction set that includes instructions/functions for ray
generation. The ray tracing instruction set can be similar to or
different from the ray-tracing instruction set supported by the ray
tracing cores 245 in FIG. 2C.
[0196] FIG. 5B illustrates exemplary internal details of an
execution unit 508, according to embodiments. A graphics execution
unit 508 can include an instruction fetch unit 537, a general
register file array (GRF) 524, an architectural register file array
(ARF) 526, a thread arbiter 522, a send unit 530, a branch unit
532, a set of SIMD floating point units (FPUs) 534, and in one
embodiment a set of dedicated integer SIMD ALUs 535. The GRF 524
and ARF 526 includes the set of general register files and
architecture register files associated with each simultaneous
hardware thread that may be active in the graphics execution unit
508. In one embodiment, per thread architectural state is
maintained in the ARF 526, while data used during thread execution
is stored in the GRF 524. The execution state of each thread,
including the instruction pointers for each thread, can be held in
thread-specific registers in the ARF 526.
[0197] In one embodiment the graphics execution unit 508 has an
architecture that is a combination of Simultaneous Multi-Threading
(SMT) and fine-grained Interleaved Multi-Threading (IMT). The
architecture has a modular configuration that can be fine-tuned at
design time based on a target number of simultaneous threads and
number of registers per execution unit, where execution unit
resources are divided across logic used to execute multiple
simultaneous threads. The number of logical threads that may be
executed by the graphics execution unit 508 is not limited to the
number of hardware threads, and multiple logical threads can be
assigned to each hardware thread.
[0198] In one embodiment, the graphics execution unit 508 can
co-issue multiple instructions, which may each be different
instructions. The thread arbiter 522 of the graphics execution unit
thread 508 can dispatch the instructions to one of the send unit
530, branch unit 532, or SIMD FPU(s) 534 for execution. Each
execution thread can access 128 general-purpose registers within
the GRF 524, where each register can store 32 bytes, accessible as
a SIMD 8-element vector of 32-bit data elements. In one embodiment,
each execution unit thread has access to 4 Kbytes within the GRF
524, although embodiments are not so limited, and greater or fewer
register resources may be provided in other embodiments. In one
embodiment the graphics execution unit 508 is partitioned into
seven hardware threads that can independently perform computational
operations, although the number of threads per execution unit can
also vary according to embodiments. For example, in one embodiment
up to 16 hardware threads are supported. In an embodiment in which
seven threads may access 4 Kbytes, the GRF 524 can store a total of
28 Kbytes. Where 16 threads may access 4 Kbytes, the GRF 524 can
store a total of 64 Kbytes. Flexible addressing modes can permit
registers to be addressed together to build effectively wider
registers or to represent strided rectangular block data
structures.
[0199] In one embodiment, memory operations, sampler operations,
and other longer-latency system communications are dispatched via
"send" instructions that are executed by the message passing send
unit 530. In one embodiment, branch instructions are dispatched to
a dedicated branch unit 532 to facilitate SIMD divergence and
eventual convergence.
[0200] In one embodiment the graphics execution unit 508 includes
one or more SIMD floating point units (FPU(s)) 534 to perform
floating-point operations. In one embodiment, the FPU(s) 534 also
support integer computation. In one embodiment the FPU(s) 534 can
SIMD execute up to M number of 32-bit floating-point (or integer)
operations, or SIMD execute up to 2M 16-bit integer or 16-bit
floating-point operations. In one embodiment, at least one of the
FPU(s) provides extended math capability to support high-throughput
transcendental math functions and double precision 54-bit
floating-point. In some embodiments, a set of 8-bit integer SIMD
ALUs 535 are also present, and may be specifically optimized to
perform operations associated with machine learning
computations.
[0201] In one embodiment, arrays of multiple instances of the
graphics execution unit 508 can be instantiated in a graphics
sub-core grouping (e.g., a sub-slice). For scalability, product
architects can choose the exact number of execution units per
sub-core grouping. In one embodiment the execution unit 508 can
execute instructions across a plurality of execution channels. In a
further embodiment, each thread executed on the graphics execution
unit 508 is executed on a different channel.
[0202] FIG. 6 illustrates an additional execution unit 600,
according to an embodiment. The execution unit 600 may be a
compute-optimized execution unit for use in, for example, a compute
engine tile 340A-340D as in FIG. 3C, but is not limited as such.
Variants of the execution unit 600 may also be used in a graphics
engine tile 310A-310D as in FIG. 3B. In one embodiment, the
execution unit 600 includes a thread control unit 601, a thread
state unit 602, an instruction fetch/prefetch unit 603, and an
instruction decode unit 604. The execution unit 600 additionally
includes a register file 606 that stores registers that can be
assigned to hardware threads within the execution unit. The
execution unit 600 additionally includes a send unit 607 and a
branch unit 608. In one embodiment, the send unit 607 and branch
unit 608 can operate similarly as the send unit 530 and a branch
unit 532 of the graphics execution unit 508 of FIG. 5B.
[0203] The execution unit 600 also includes a compute unit 610 that
includes multiple different types of functional units. In one
embodiment the compute unit 610 includes an ALU unit 611 that
includes an array of arithmetic logic units. The ALU unit 611 can
be configured to perform 64-bit, 32-bit, and 16-bit integer and
floating point operations. Integer and floating point operations
may be performed simultaneously. The compute unit 610 can also
include a systolic array 612, and a math unit 613. The systolic
array 612 includes a W wide and D deep network of data processing
units that can be used to perform vector or other data-parallel
operations in a systolic manner. In one embodiment the systolic
array 612 can be configured to perform matrix operations, such as
matrix dot product operations. In one embodiment the systolic array
612 support 16-bit floating point operations, as well as 8-bit and
4-bit integer operations. In one embodiment the systolic array 612
can be configured to accelerate machine learning operations. In
such embodiments, the systolic array 612 can be configured with
support for the bfloat 16-bit floating point format. In one
embodiment, a math unit 613 can be included to perform a specific
subset of mathematical operations in an efficient and lower-power
manner than then ALU unit 611. The math unit 613 can include a
variant of math logic that may be found in shared function logic of
a graphics processing engine provided by other embodiments (e.g.,
math logic 422 of the shared function logic 420 of FIG. 4). In one
embodiment the math unit 613 can be configured to perform 32-bit
and 64-bit floating point operations.
[0204] The thread control unit 601 includes logic to control the
execution of threads within the execution unit. The thread control
unit 601 can include thread arbitration logic to start, stop, and
preempt execution of threads within the execution unit 600. The
thread state unit 602 can be used to store thread state for threads
assigned to execute on the execution unit 600. Storing the thread
state within the execution unit 600 enables the rapid pre-emption
of threads when those threads become blocked or idle. The
instruction fetch/prefetch unit 603 can fetch instructions from an
instruction cache of higher level execution logic (e.g.,
instruction cache 506 as in FIG. 5A). The instruction
fetch/prefetch unit 603 can also issue prefetch requests for
instructions to be loaded into the instruction cache based on an
analysis of currently executing threads. The instruction decode
unit 604 can be used to decode instructions to be executed by the
compute units. In one embodiment, the instruction decode unit 604
can be used as a secondary decoder to decode complex instructions
into constituent micro-operations.
[0205] The execution unit 600 additionally includes a register file
606 that can be used by hardware threads executing on the execution
unit 600. Registers in the register file 606 can be divided across
the logic used to execute multiple simultaneous threads within the
compute unit 610 of the execution unit 600. The number of logical
threads that may be executed by the graphics execution unit 600 is
not limited to the number of hardware threads, and multiple logical
threads can be assigned to each hardware thread. The size of the
register file 606 can vary across embodiments based on the number
of supported hardware threads. In one embodiment, register renaming
may be used to dynamically allocate registers to hardware
threads.
[0206] FIG. 7 is a block diagram illustrating a graphics processor
instruction formats 700 according to some embodiments. In one or
more embodiment, the graphics processor execution units support an
instruction set having instructions in multiple formats. The solid
lined boxes illustrate the components that are generally included
in an execution unit instruction, while the dashed lines include
components that are optional or that are only included in a sub-set
of the instructions. In some embodiments, instruction format 700
described and illustrated are macro-instructions, in that they are
instructions supplied to the execution unit, as opposed to
micro-operations resulting from instruction decode once the
instruction is processed.
[0207] In some embodiments, the graphics processor execution units
natively support instructions in a 128-bit instruction format 710.
A 64-bit compacted instruction format 730 is available for some
instructions based on the selected instruction, instruction
options, and number of operands. The native 128-bit instruction
format 710 provides access to all instruction options, while some
options and operations are restricted in the 64-bit format 730. The
native instructions available in the 64-bit format 730 vary by
embodiment. In some embodiments, the instruction is compacted in
part using a set of index values in an index field 713. The
execution unit hardware references a set of compaction tables based
on the index values and uses the compaction table outputs to
reconstruct a native instruction in the 128-bit instruction format
710. Other sizes and formats of instruction can be used.
[0208] For each format, instruction opcode 712 defines the
operation that the execution unit is to perform. The execution
units execute each instruction in parallel across the multiple data
elements of each operand. For example, in response to an add
instruction the execution unit performs a simultaneous add
operation across each color channel representing a texture element
or picture element. By default, the execution unit performs each
instruction across all data channels of the operands. In some
embodiments, instruction control field 714 enables control over
certain execution options, such as channels selection (e.g.,
predication) and data channel order (e.g., swizzle). For
instructions in the 128-bit instruction format 710 an exec-size
field 716 limits the number of data channels that will be executed
in parallel. In some embodiments, exec-size field 716 is not
available for use in the 64-bit compact instruction format 730.
[0209] Some execution unit instructions have up to three operands
including two source operands, src0 720, src1 722, and one
destination 718. In some embodiments, the execution units support
dual destination instructions, where one of the destinations is
implied. Data manipulation instructions can have a third source
operand (e.g., SRC2 724), where the instruction opcode 712
determines the number of source operands. An instruction's last
source operand can be an immediate (e.g., hard-coded) value passed
with the instruction.
[0210] In some embodiments, the 128-bit instruction format 710
includes an access/address mode field 726 specifying, for example,
whether direct register addressing mode or indirect register
addressing mode is used. When direct register addressing mode is
used, the register address of one or more operands is directly
provided by bits in the instruction.
[0211] In some embodiments, the 128-bit instruction format 710
includes an access/address mode field 726, which specifies an
address mode and/or an access mode for the instruction. In one
embodiment the access mode is used to define a data access
alignment for the instruction. Some embodiments support access
modes including a 16-byte aligned access mode and a 1-byte aligned
access mode, where the byte alignment of the access mode determines
the access alignment of the instruction operands. For example, when
in a first mode, the instruction may use byte-aligned addressing
for source and destination operands and when in a second mode, the
instruction may use 16-byte-aligned addressing for all source and
destination operands.
[0212] In one embodiment, the address mode portion of the
access/address mode field 726 determines whether the instruction is
to use direct or indirect addressing. When direct register
addressing mode is used bits in the instruction directly provide
the register address of one or more operands. When indirect
register addressing mode is used, the register address of one or
more operands may be computed based on an address register value
and an address immediate field in the instruction.
[0213] In some embodiments instructions are grouped based on opcode
712 bit-fields to simplify Opcode decode 740. For an 8-bit opcode,
bits 4, 5, and 6 allow the execution unit to determine the type of
opcode. The precise opcode grouping shown is merely an example. In
some embodiments, a move and logic opcode group 742 includes data
movement and logic instructions (e.g., move (mov), compare (cmp)).
In some embodiments, move and logic group 742 shares the five most
significant bits (MSB), where move (mov) instructions are in the
form of 0000xxxxb and logic instructions are in the form of
0001xxxxb. A flow control instruction group 744 (e.g., call, jump
(jmp)) includes instructions in the form of 0010xxxxb (e.g., 0x20).
A miscellaneous instruction group 746 includes a mix of
instructions, including synchronization instructions (e.g., wait,
send) in the form of 0011xxxxb (e.g., 0x30). A parallel math
instruction group 748 includes component-wise arithmetic
instructions (e.g., add, multiply (mul)) in the form of 0100xxxxb
(e.g., 0x40). The parallel math group 748 performs the arithmetic
operations in parallel across data channels. The vector math group
750 includes arithmetic instructions (e.g., dp4) in the form of
0101xxxxb (e.g., 0x50). The vector math group performs arithmetic
such as dot product calculations on vector operands. The
illustrated opcode decode 740, in one embodiment, can be used to
determine which portion of an execution unit will be used to
execute a decoded instruction. For example, some instructions may
be designated as systolic instructions that will be performed by a
systolic array. Other instructions, such as ray-tracing
instructions (not shown) can be routed to a ray-tracing core or
ray-tracing logic within a slice or partition of execution
logic.
[0214] Graphics Pipeline
[0215] FIG. 8 is a block diagram of another embodiment of a
graphics processor 800. Elements of FIG. 8 having the same
reference numbers (or names) as the elements of any other figure
herein can operate or function in any manner similar to that
described elsewhere herein, but are not limited to such.
[0216] In some embodiments, graphics processor 800 includes a
geometry pipeline 820, a media pipeline 830, a display engine 840,
thread execution logic 850, and a render output pipeline 870. In
some embodiments, graphics processor 800 is a graphics processor
within a multi-core processing system that includes one or more
general-purpose processing cores. The graphics processor is
controlled by register writes to one or more control registers (not
shown) or via commands issued to graphics processor 800 via a ring
interconnect 802. In some embodiments, ring interconnect 802
couples graphics processor 800 to other processing components, such
as other graphics processors or general-purpose processors.
Commands from ring interconnect 802 are interpreted by a command
streamer 803, which supplies instructions to individual components
of the geometry pipeline 820 or the media pipeline 830.
[0217] In some embodiments, command streamer 803 directs the
operation of a vertex fetcher 805 that reads vertex data from
memory and executes vertex-processing commands provided by command
streamer 803. In some embodiments, vertex fetcher 805 provides
vertex data to a vertex shader 807, which performs coordinate space
transformation and lighting operations to each vertex. In some
embodiments, vertex fetcher 805 and vertex shader 807 execute
vertex-processing instructions by dispatching execution threads to
execution units 852A-852B via a thread dispatcher 831.
[0218] In some embodiments, execution units 852A-852B are an array
of vector processors having an instruction set for performing
graphics and media operations. In some embodiments, execution units
852A-852B have an attached L1 cache 851 that is specific for each
array or shared between the arrays. The cache can be configured as
a data cache, an instruction cache, or a single cache that is
partitioned to contain data and instructions in different
partitions.
[0219] In some embodiments, geometry pipeline 820 includes
tessellation components to perform hardware-accelerated
tessellation of 3D objects. In some embodiments, a programmable
hull shader 811 configures the tessellation operations. A
programmable domain shader 817 provides back-end evaluation of
tessellation output. A tessellator 813 operates at the direction of
hull shader 811 and contains special purpose logic to generate a
set of detailed geometric objects based on a coarse geometric model
that is provided as input to geometry pipeline 820. In some
embodiments, if tessellation is not used, tessellation components
(e.g., hull shader 811, tessellator 813, and domain shader 817) can
be bypassed.
[0220] In some embodiments, complete geometric objects can be
processed by a geometry shader 819 via one or more threads
dispatched to execution units 852A-852B, or can proceed directly to
the clipper 829. In some embodiments, the geometry shader operates
on entire geometric objects, rather than vertices or patches of
vertices as in previous stages of the graphics pipeline. If the
tessellation is disabled the geometry shader 819 receives input
from the vertex shader 807. In some embodiments, geometry shader
819 is programmable by a geometry shader program to perform
geometry tessellation if the tessellation units are disabled.
[0221] Before rasterization, a clipper 829 processes vertex data.
The clipper 829 may be a fixed function clipper or a programmable
clipper having clipping and geometry shader functions. In some
embodiments, a rasterizer and depth test component 873 in the
render output pipeline 870 dispatches pixel shaders to convert the
geometric objects into per pixel representations. In some
embodiments, pixel shader logic is included in thread execution
logic 850. In some embodiments, an application can bypass the
rasterizer and depth test component 873 and access un-rasterized
vertex data via a stream out unit 823.
[0222] The graphics processor 800 has an interconnect bus,
interconnect fabric, or some other interconnect mechanism that
allows data and message passing amongst the major components of the
processor. In some embodiments, execution units 852A-852B and
associated logic units (e.g., L1 cache 851, sampler 854, texture
cache 858, etc.) interconnect via a data port 856 to perform memory
access and communicate with render output pipeline components of
the processor. In some embodiments, sampler 854, caches 851, 858
and execution units 852A-852B each have separate memory access
paths. In one embodiment the texture cache 858 can also be
configured as a sampler cache.
[0223] In some embodiments, render output pipeline 870 contains a
rasterizer and depth test component 873 that converts vertex-based
objects into an associated pixel-based representation. In some
embodiments, the rasterizer logic includes a windower/masker unit
to perform fixed function triangle and line rasterization. An
associated render cache 878 and depth cache 879 are also available
in some embodiments. A pixel operations component 877 performs
pixel-based operations on the data, though in some instances, pixel
operations associated with 2D operations (e.g. bit block image
transfers with blending) are performed by the 2D engine 841, or
substituted at display time by the display controller 843 using
overlay display planes. In some embodiments, a shared L3 cache 875
is available to all graphics components, allowing the sharing of
data without the use of main system memory.
[0224] In some embodiments, graphics processor media pipeline 830
includes a media engine 837 and a video front-end 834. In some
embodiments, video front-end 834 receives pipeline commands from
the command streamer 803. In some embodiments, media pipeline 830
includes a separate command streamer. In some embodiments, video
front-end 834 processes media commands before sending the command
to the media engine 837. In some embodiments, media engine 837
includes thread spawning functionality to spawn threads for
dispatch to thread execution logic 850 via thread dispatcher
831.
[0225] In some embodiments, graphics processor 800 includes a
display engine 840. In some embodiments, display engine 840 is
external to processor 800 and couples with the graphics processor
via the ring interconnect 802, or some other interconnect bus or
fabric. In some embodiments, display engine 840 includes a 2D
engine 841 and a display controller 843. In some embodiments,
display engine 840 contains special purpose logic capable of
operating independently of the 3D pipeline. In some embodiments,
display controller 843 couples with a display device (not shown),
which may be a system integrated display device, as in a laptop
computer, or an external display device attached via a display
device connector.
[0226] In some embodiments, the geometry pipeline 820 and media
pipeline 830 are configurable to perform operations based on
multiple graphics and media programming interfaces and are not
specific to any one application programming interface (API). In
some embodiments, driver software for the graphics processor
translates API calls that are specific to a particular graphics or
media library into commands that can be processed by the graphics
processor. In some embodiments, support is provided for the Open
Graphics Library (OpenGL), Open Computing Language (OpenCL), and/or
Vulkan graphics and compute API, all from the Khronos Group. In
some embodiments, support may also be provided for the Direct3D
library from the Microsoft Corporation. In some embodiments, a
combination of these libraries may be supported. Support may also
be provided for the Open Source Computer Vision Library (OpenCV). A
future API with a compatible 3D pipeline would also be supported if
a mapping can be made from the pipeline of the future API to the
pipeline of the graphics processor.
[0227] Graphics Pipeline Programming
[0228] FIG. 9A is a block diagram illustrating a graphics processor
command format 900 according to some embodiments. FIG. 9B is a
block diagram illustrating a graphics processor command sequence
910 according to an embodiment. The solid lined boxes in FIG. 9A
illustrate the components that are generally included in a graphics
command while the dashed lines include components that are optional
or that are only included in a sub-set of the graphics commands.
The exemplary graphics processor command format 900 of FIG. 9A
includes data fields to identify a client 902, a command operation
code (opcode) 904, and data 906 for the command. A sub-opcode 905
and a command size 908 are also included in some commands.
[0229] In some embodiments, client 902 specifies the client unit of
the graphics device that processes the command data. In some
embodiments, a graphics processor command parser examines the
client field of each command to condition the further processing of
the command and route the command data to the appropriate client
unit. In some embodiments, the graphics processor client units
include a memory interface unit, a render unit, a 2D unit, a 3D
unit, and a media unit. Each client unit has a corresponding
processing pipeline that processes the commands. Once the command
is received by the client unit, the client unit reads the opcode
904 and, if present, sub-opcode 905 to determine the operation to
perform. The client unit performs the command using information in
data field 906. For some commands an explicit command size 908 is
expected to specify the size of the command. In some embodiments,
the command parser automatically determines the size of at least
some of the commands based on the command opcode. In some
embodiments commands are aligned via multiples of a double word.
Other command formats can be used.
[0230] The flow diagram in FIG. 9B illustrates an exemplary
graphics processor command sequence 910. In some embodiments,
software or firmware of a data processing system that features an
embodiment of a graphics processor uses a version of the command
sequence shown to set up, execute, and terminate a set of graphics
operations. A sample command sequence is shown and described for
purposes of example only as embodiments are not limited to these
specific commands or to this command sequence. Moreover, the
commands may be issued as batch of commands in a command sequence,
such that the graphics processor will process the sequence of
commands in at least partially concurrence.
[0231] In some embodiments, the graphics processor command sequence
910 may begin with a pipeline flush command 912 to cause any active
graphics pipeline to complete the currently pending commands for
the pipeline. In some embodiments, the 3D pipeline 922 and the
media pipeline 924 do not operate concurrently. The pipeline flush
is performed to cause the active graphics pipeline to complete any
pending commands. In response to a pipeline flush, the command
parser for the graphics processor will pause command processing
until the active drawing engines complete pending operations and
the relevant read caches are invalidated. Optionally, any data in
the render cache that is marked `dirty` can be flushed to memory.
In some embodiments, pipeline flush command 912 can be used for
pipeline synchronization or before placing the graphics processor
into a low power state.
[0232] In some embodiments, a pipeline select command 913 is used
when a command sequence requires the graphics processor to
explicitly switch between pipelines. In some embodiments, a
pipeline select command 913 is required only once within an
execution context before issuing pipeline commands unless the
context is to issue commands for both pipelines. In some
embodiments, a pipeline flush command 912 is required immediately
before a pipeline switch via the pipeline select command 913.
[0233] In some embodiments, a pipeline control command 914
configures a graphics pipeline for operation and is used to program
the 3D pipeline 922 and the media pipeline 924. In some
embodiments, pipeline control command 914 configures the pipeline
state for the active pipeline. In one embodiment, the pipeline
control command 914 is used for pipeline synchronization and to
clear data from one or more cache memories within the active
pipeline before processing a batch of commands.
[0234] In some embodiments, return buffer state commands 916 are
used to configure a set of return buffers for the respective
pipelines to write data. Some pipeline operations require the
allocation, selection, or configuration of one or more return
buffers into which the operations write intermediate data during
processing. In some embodiments, the graphics processor also uses
one or more return buffers to store output data and to perform
cross thread communication. In some embodiments, the return buffer
state 916 includes selecting the size and number of return buffers
to use for a set of pipeline operations.
[0235] The remaining commands in the command sequence differ based
on the active pipeline for operations. Based on a pipeline
determination 920, the command sequence is tailored to the 3D
pipeline 922 beginning with the 3D pipeline state 930 or the media
pipeline 924 beginning at the media pipeline state 940.
[0236] The commands to configure the 3D pipeline state 930 include
3D state setting commands for vertex buffer state, vertex element
state, constant color state, depth buffer state, and other state
variables that are to be configured before 3D primitive commands
are processed. The values of these commands are determined at least
in part based on the particular 3D API in use. In some embodiments,
3D pipeline state 930 commands are also able to selectively disable
or bypass certain pipeline elements if those elements will not be
used.
[0237] In some embodiments, 3D primitive 932 command is used to
submit 3D primitives to be processed by the 3D pipeline. Commands
and associated parameters that are passed to the graphics processor
via the 3D primitive 932 command are forwarded to the vertex fetch
function in the graphics pipeline. The vertex fetch function uses
the 3D primitive 932 command data to generate vertex data
structures. The vertex data structures are stored in one or more
return buffers. In some embodiments, 3D primitive 932 command is
used to perform vertex operations on 3D primitives via vertex
shaders. To process vertex shaders, 3D pipeline 922 dispatches
shader execution threads to graphics processor execution units.
[0238] In some embodiments, 3D pipeline 922 is triggered via an
execute 934 command or event. In some embodiments, a register write
triggers command execution. In some embodiments execution is
triggered via a `go` or `kick` command in the command sequence. In
one embodiment, command execution is triggered using a pipeline
synchronization command to flush the command sequence through the
graphics pipeline. The 3D pipeline will perform geometry processing
for the 3D primitives. Once operations are complete, the resulting
geometric objects are rasterized and the pixel engine colors the
resulting pixels. Additional commands to control pixel shading and
pixel back end operations may also be included for those
operations.
[0239] In some embodiments, the graphics processor command sequence
910 follows the media pipeline 924 path when performing media
operations. In general, the specific use and manner of programming
for the media pipeline 924 depends on the media or compute
operations to be performed. Specific media decode operations may be
offloaded to the media pipeline during media decode. In some
embodiments, the media pipeline can also be bypassed and media
decode can be performed in whole or in part using resources
provided by one or more general-purpose processing cores. In one
embodiment, the media pipeline also includes elements for
general-purpose graphics processor unit (GPGPU) operations, where
the graphics processor is used to perform SIMD vector operations
using computational shader programs that are not explicitly related
to the rendering of graphics primitives.
[0240] In some embodiments, media pipeline 924 is configured in a
similar manner as the 3D pipeline 922. A set of commands to
configure the media pipeline state 940 are dispatched or placed
into a command queue before the media object commands 942. In some
embodiments, commands for the media pipeline state 940 include data
to configure the media pipeline elements that will be used to
process the media objects. This includes data to configure the
video decode and video encode logic within the media pipeline, such
as encode or decode format. In some embodiments, commands for the
media pipeline state 940 also support the use of one or more
pointers to "indirect" state elements that contain a batch of state
settings.
[0241] In some embodiments, media object commands 942 supply
pointers to media objects for processing by the media pipeline. The
media objects include memory buffers containing video data to be
processed. In some embodiments, all media pipeline states must be
valid before issuing a media object command 942. Once the pipeline
state is configured and media object commands 942 are queued, the
media pipeline 924 is triggered via an execute command 944 or an
equivalent execute event (e.g., register write). Output from media
pipeline 924 may then be post processed by operations provided by
the 3D pipeline 922 or the media pipeline 924. In some embodiments,
GPGPU operations are configured and executed in a similar manner as
media operations.
[0242] Graphics Software Architecture
[0243] FIG. 10 illustrates an exemplary graphics software
architecture for a data processing system 1000 according to some
embodiments. In some embodiments, software architecture includes a
3D graphics application 1010, an operating system 1020, and at
least one processor 1030. In some embodiments, processor 1030
includes a graphics processor 1032 and one or more general-purpose
processor core(s) 1034. The graphics application 1010 and operating
system 1020 each execute in the system memory 1050 of the data
processing system.
[0244] In some embodiments, 3D graphics application 1010 contains
one or more shader programs including shader instructions 1012. The
shader language instructions may be in a high-level shader
language, such as the High-Level Shader Language (HLSL) of
Direct3D, the OpenGL Shader Language (GLSL), and so forth. The
application also includes executable instructions 1014 in a machine
language suitable for execution by the general-purpose processor
core 1034. The application also includes graphics objects 1016
defined by vertex data.
[0245] In some embodiments, operating system 1020 is a
Microsoft.RTM. Windows.RTM. operating system from the Microsoft
Corporation, a proprietary UNIX-like operating system, or an open
source UNIX-like operating system using a variant of the Linux
kernel. The operating system 1020 can support a graphics API 1022
such as the Direct3D API, the OpenGL API, or the Vulkan API. When
the Direct3D API is in use, the operating system 1020 uses a
front-end shader compiler 1024 to compile any shader instructions
1012 in HLSL into a lower-level shader language. The compilation
may be a just-in-time (JIT) compilation or the application can
perform shader pre-compilation. In some embodiments, high-level
shaders are compiled into low-level shaders during the compilation
of the 3D graphics application 1010. In some embodiments, the
shader instructions 1012 are provided in an intermediate form, such
as a version of the Standard Portable Intermediate Representation
(SPIR) used by the Vulkan API.
[0246] In some embodiments, user mode graphics driver 1026 contains
a back-end shader compiler xxxx to convert the shader instructions
1012 into a hardware specific representation. When the OpenGL API
is in use, shader instructions 1012 in the GLSL high-level language
are passed to a user mode graphics driver 1026 for compilation. In
some embodiments, user mode graphics driver 1026 uses operating
system kernel mode functions 1028 to communicate with a kernel mode
graphics driver 1029. In some embodiments, kernel mode graphics
driver 1029 communicates with graphics processor 1032 to dispatch
commands and instructions.
[0247] IP Core Implementations
[0248] One or more aspects of at least one embodiment may be
implemented by representative code stored on a machine-readable
medium which represents and/or defines logic within an integrated
circuit such as a processor. For example, the machine-readable
medium may include instructions which represent various logic
within the processor. When read by a machine, the instructions may
cause the machine to fabricate the logic to perform the techniques
described herein. Such representations, known as "IP cores," are
reusable units of logic for an integrated circuit that may be
stored on a tangible, machine-readable medium as a hardware model
that describes the structure of the integrated circuit. The
hardware model may be supplied to various customers or
manufacturing facilities, which load the hardware model on
fabrication machines that manufacture the integrated circuit. The
integrated circuit may be fabricated such that the circuit performs
operations described in association with any of the embodiments
described herein.
[0249] FIG. 11A is a block diagram illustrating an IP core
development system 1100 that may be used to manufacture an
integrated circuit to perform operations according to an
embodiment. The IP core development system 1100 may be used to
generate modular, re-usable designs that can be incorporated into a
larger design or used to construct an entire integrated circuit
(e.g., an SOC integrated circuit). A design facility 1130 can
generate a software simulation 1110 of an IP core design in a
high-level programming language (e.g., C/C++). The software
simulation 1110 can be used to design, test, and verify the
behavior of the IP core using a simulation model 1112. The
simulation model 1112 may include functional, behavioral, and/or
timing simulations. A register transfer level (RTL) design 1115 can
then be created or synthesized from the simulation model 1112. The
RTL design 1115 is an abstraction of the behavior of the integrated
circuit that models the flow of digital signals between hardware
registers, including the associated logic performed using the
modeled digital signals. In addition to an RTL design 1115,
lower-level designs at the logic level or transistor level may also
be created, designed, or synthesized. Thus, the particular details
of the initial design and simulation may vary.
[0250] The RTL design 1115 or equivalent may be further synthesized
by the design facility into a hardware model 1120, which may be in
a hardware description language (HDL), or some other representation
of physical design data. The HDL may be further simulated or tested
to verify the IP core design. The IP core design can be stored for
delivery to a 3rd party fabrication facility 1165 using
non-volatile memory 1140 (e.g., hard disk, flash memory, or any
non-volatile storage medium). Alternatively, the IP core design may
be transmitted (e.g., via the Internet) over a wired connection
1150 or wireless connection 1160. The fabrication facility 1165 may
then fabricate an integrated circuit that is based at least in part
on the IP core design. The fabricated integrated circuit can be
configured to perform operations in accordance with at least one
embodiment described herein.
[0251] FIG. 11B illustrates a cross-section side view of an
integrated circuit package assembly 1170, according to some
embodiments described herein. The integrated circuit package
assembly 1170 illustrates an implementation of one or more
processor or accelerator devices as described herein. The package
assembly 1170 includes multiple units of hardware logic 1172, 1174
connected to a substrate 1180. The logic 1172, 1174 may be
implemented at least partly in configurable logic or
fixed-functionality logic hardware, and can include one or more
portions of any of the processor core(s), graphics processor(s), or
other accelerator devices described herein. Each unit of logic
1172, 1174 can be implemented within a semiconductor die and
coupled with the substrate 1180 via an interconnect structure 1173.
The interconnect structure 1173 may be configured to route
electrical signals between the logic 1172, 1174 and the substrate
1180, and can include interconnects such as, but not limited to
bumps or pillars. In some embodiments, the interconnect structure
1173 may be configured to route electrical signals such as, for
example, input/output (I/O) signals and/or power or ground signals
associated with the operation of the logic 1172, 1174. In some
embodiments, the substrate 1180 is an epoxy-based laminate
substrate. The substrate 1180 may include other suitable types of
substrates in other embodiments. The package assembly 1170 can be
connected to other electrical devices via a package interconnect
1183. The package interconnect 1183 may be coupled to a surface of
the substrate 1180 to route electrical signals to other electrical
devices, such as a motherboard, other chipset, or multi-chip
module.
[0252] In some embodiments, the units of logic 1172, 1174 are
electrically coupled with a bridge 1182 that is configured to route
electrical signals between the logic 1172, 1174. The bridge 1182
may be a dense interconnect structure that provides a route for
electrical signals. The bridge 1182 may include a bridge substrate
composed of glass or a suitable semiconductor material. Electrical
routing features can be formed on the bridge substrate to provide a
chip-to-chip connection between the logic 1172, 1174.
[0253] Although two units of logic 1172, 1174 and a bridge 1182 are
illustrated, embodiments described herein may include more or fewer
logic units on one or more dies. The one or more dies may be
connected by zero or more bridges, as the bridge 1182 may be
excluded when the logic is included on a single die. Alternatively,
multiple dies or units of logic can be connected by one or more
bridges. Additionally, multiple logic units, dies, and bridges can
be connected together in other possible configurations, including
three-dimensional configurations.
[0254] FIG. 11C illustrates a package assembly 1190 that includes
multiple units of hardware logic chiplets connected to a substrate
1180 (e.g., base die). A graphics processing unit, parallel
processor, and/or compute accelerator as described herein can be
composed from diverse silicon chiplets that are separately
manufactured. In this context, a chiplet is an at least partially
packaged integrated circuit that includes distinct units of logic
that can be assembled with other chiplets into a larger package. A
diverse set of chiplets with different IP core logic can be
assembled into a single device. Additionally the chiplets can be
integrated into a base die or base chiplet using active interposer
technology. The concepts described herein enable the
interconnection and communication between the different forms of IP
within the GPU. IP cores can be manufactured using different
process technologies and composed during manufacturing, which
avoids the complexity of converging multiple IPs, especially on a
large SoC with several flavors IPs, to the same manufacturing
process. Enabling the use of multiple process technologies improves
the time to market and provides a cost-effective way to create
multiple product SKUs. Additionally, the disaggregated IPs are more
amenable to being power gated independently, components that are
not in use on a given workload can be powered off, reducing overall
power consumption.
[0255] The hardware logic chiplets can include special purpose
hardware logic chiplets 1172, logic or I/O chiplets 1174, and/or
memory chiplets 1175. The hardware logic chiplets 1172 and logic or
I/O chiplets 1174 may be implemented at least partly in
configurable logic or fixed-functionality logic hardware and can
include one or more portions of any of the processor core(s),
graphics processor(s), parallel processors, or other accelerator
devices described herein. The memory chiplets 1175 can be DRAM
(e.g., GDDR, HBM) memory or cache (SRAM) memory.
[0256] Each chiplet can be fabricated as separate semiconductor die
and coupled with the substrate 1180 via an interconnect structure
1173. The interconnect structure 1173 may be configured to route
electrical signals between the various chiplets and logic within
the substrate 1180. The interconnect structure 1173 can include
interconnects such as, but not limited to bumps or pillars. In some
embodiments, the interconnect structure 1173 may be configured to
route electrical signals such as, for example, input/output (I/O)
signals and/or power or ground signals associated with the
operation of the logic, I/O and memory chiplets.
[0257] In some embodiments, the substrate 1180 is an epoxy-based
laminate substrate. The substrate 1180 may include other suitable
types of substrates in other embodiments. The package assembly 1190
can be connected to other electrical devices via a package
interconnect 1183. The package interconnect 1183 may be coupled to
a surface of the substrate 1180 to route electrical signals to
other electrical devices, such as a motherboard, other chipset, or
multi-chip module.
[0258] In some embodiments, a logic or I/O chiplet 1174 and a
memory chiplet 1175 can be electrically coupled via a bridge 1187
that is configured to route electrical signals between the logic or
I/O chiplet 1174 and a memory chiplet 1175. The bridge 1187 may be
a dense interconnect structure that provides a route for electrical
signals. The bridge 1187 may include a bridge substrate composed of
glass or a suitable semiconductor material. Electrical routing
features can be formed on the bridge substrate to provide a
chip-to-chip connection between the logic or I/O chiplet 1174 and a
memory chiplet 1175. The bridge 1187 may also be referred to as a
silicon bridge or an interconnect bridge. For example, the bridge
1187, in some embodiments, is an Embedded Multi-die Interconnect
Bridge (EMIB). In some embodiments, the bridge 1187 may simply be a
direct connection from one chiplet to another chiplet.
[0259] The substrate 1180 can include hardware components for I/O
1191, cache memory 1192, and other hardware logic 1193. A fabric
1185 can be embedded in the substrate 1180 to enable communication
between the various logic chiplets and the logic 1191, 1193 within
the substrate 1180. In one embodiment, the I/O 1191, fabric 1185,
cache, bridge, and other hardware logic 1193 can be integrated into
a base die that is layered on top of the substrate 1180.
[0260] In various embodiments a package assembly 1190 can include
fewer or greater number of components and chiplets that are
interconnected by a fabric 1185 or one or more bridges 1187. The
chiplets within the package assembly 1190 may be arranged in a 3D
or 2.5D arrangement. In general, bridge structures 1187 may be used
to facilitate a point to point interconnect between, for example,
logic or I/O chiplets and memory chiplets. The fabric 1185 can be
used to interconnect the various logic and/or I/O chiplets (e.g.,
chiplets 1172, 1174, 1191, 1193). with other logic and/or I/O
chiplets. In one embodiment, the cache memory 1192 within the
substrate can act as a global cache for the package assembly 1190,
part of a distributed global cache, or as a dedicated cache for the
fabric 1185.
[0261] FIG. 11D illustrates a package assembly 1194 including
interchangeable chiplets 1195, according to an embodiment. The
interchangeable chiplets 1195 can be assembled into standardized
slots on one or more base chiplets 1196, 1198. The base chiplets
1196, 1198 can be coupled via a bridge interconnect 1197, which can
be similar to the other bridge interconnects described herein and
may be, for example, an EMIB. Memory chiplets can also be connected
to logic or I/O chiplets via a bridge interconnect. I/O and logic
chiplets can communicate via an interconnect fabric. The base
chiplets can each support one or more slots in a standardized
format for one of logic or I/O or memory/cache.
[0262] In one embodiment, SRAM and power delivery circuits can be
fabricated into one or more of the base chiplets 1196, 1198, which
can be fabricated using a different process technology relative to
the interchangeable chiplets 1195 that are stacked on top of the
base chiplets. For example, the base chiplets 1196, 1198 can be
fabricated using a larger process technology, while the
interchangeable chiplets can be manufactured using a smaller
process technology. One or more of the interchangeable chiplets
1195 may be memory (e.g., DRAM) chiplets. Different memory
densities can be selected for the package assembly 1194 based on
the power, and/or performance targeted for the product that uses
the package assembly 1194. Additionally, logic chiplets with a
different number of type of functional units can be selected at
time of assembly based on the power, and/or performance targeted
for the product. Additionally, chiplets containing IP logic cores
of differing types can be inserted into the interchangeable chiplet
slots, enabling hybrid processor designs that can mix and match
different technology IP blocks.
[0263] Exemplary System on a Chip Integrated Circuit
[0264] FIGS. 12-13 illustrate exemplary integrated circuits and
associated graphics processors that may be fabricated using one or
more IP cores, according to various embodiments described herein.
In addition to what is illustrated, other logic and circuits may be
included, including additional graphics processors/cores,
peripheral interface controllers, or general-purpose processor
cores.
[0265] FIG. 12 is a block diagram illustrating an exemplary system
on a chip integrated circuit 1200 that may be fabricated using one
or more IP cores, according to an embodiment. Exemplary integrated
circuit 1200 includes one or more application processor(s) 1205
(e.g., CPUs), at least one graphics processor 1210, and may
additionally include an image processor 1215 and/or a video
processor 1220, any of which may be a modular IP core from the same
or multiple different design facilities. Integrated circuit 1200
includes peripheral or bus logic including a USB controller 1225,
UART controller 1230, an SPI/SDIO controller 1235, and an I2S/I2C
controller 1240. Additionally, the integrated circuit can include a
display device 1245 coupled to one or more of a high-definition
multimedia interface (HDMI) controller 1250 and a mobile industry
processor interface (MIPI) display interface 1255. Storage may be
provided by a flash memory subsystem 1260 including flash memory
and a flash memory controller. Memory interface may be provided via
a memory controller 1265 for access to SDRAM or SRAM memory
devices. Some integrated circuits additionally include an embedded
security engine 1270.
[0266] FIGS. 13-14 are block diagrams illustrating exemplary
graphics processors for use within an SoC, according to embodiments
described herein. FIG. 13 illustrates an exemplary graphics
processor 1310 of a system on a chip integrated circuit that may be
fabricated using one or more IP cores, according to an embodiment.
FIG. 13B illustrates an additional exemplary graphics processor
1340 of a system on a chip integrated circuit that may be
fabricated using one or more IP cores, according to an embodiment.
Graphics processor 1310 of FIG. 13 is an example of a low power
graphics processor core. Graphics processor 1340 of FIG. 13B is an
example of a higher performance graphics processor core. Each of
the graphics processors 1310, 1340 can be variants of the graphics
processor 1210 of FIG. 12.
[0267] As shown in FIG. 13, graphics processor 1310 includes a
vertex processor 1305 and one or more fragment processor(s)
1315A-1315N (e.g., 1315A, 1315B, 1315C, 1315D, through 1315N-1, and
1315N). Graphics processor 1310 can execute different shader
programs via separate logic, such that the vertex processor 1305 is
optimized to execute operations for vertex shader programs, while
the one or more fragment processor(s) 1315A-1315N execute fragment
(e.g., pixel) shading operations for fragment or pixel shader
programs. The vertex processor 1305 performs the vertex processing
stage of the 3D graphics pipeline and generates primitives and
vertex data. The fragment processor(s) 1315A-1315N use the
primitive and vertex data generated by the vertex processor 1305 to
produce a framebuffer that is displayed on a display device. In one
embodiment, the fragment processor(s) 1315A-1315N are optimized to
execute fragment shader programs as provided for in the OpenGL API,
which may be used to perform similar operations as a pixel shader
program as provided for in the Direct 3D API.
[0268] Graphics processor 1310 additionally includes one or more
memory management units (MMUs) 1320A-1320B, cache(s) 1325A-1325B,
and circuit interconnect(s) 1330A-1330B. The one or more MMU(s)
1320A-1320B provide for virtual to physical address mapping for the
graphics processor 1310, including for the vertex processor 1305
and/or fragment processor(s) 1315A-1315N, which may reference
vertex or image/texture data stored in memory, in addition to
vertex or image/texture data stored in the one or more cache(s)
1325A-1325B. In one embodiment the one or more MMU(s) 1320A-1320B
may be synchronized with other MMUs within the system, including
one or more MMUs associated with the one or more application
processor(s) 1205, image processor 1215, and/or video processor
1220 of FIG. 12, such that each processor 1205-1220 can participate
in a shared or unified virtual memory system. The one or more
circuit interconnect(s) 1330A-1330B enable graphics processor 1310
to interface with other IP cores within the SoC, either via an
internal bus of the SoC or via a direct connection, according to
embodiments.
[0269] As shown FIG. 14, graphics processor 1340 includes the one
or more MMU(s) 1320A-1320B, cache(s) 1325A-1325B, and circuit
interconnect(s) 1330A-1330B of the graphics processor 1310 of FIG.
13A. Graphics processor 1340 includes one or more shader core(s)
1355A-1355N (e.g., 1455A, 1355B, 1355C, 1355D, 1355E, 1355F,
through 1355N-1, and 1355N), which provides for a unified shader
core architecture in which a single core or type or core can
execute all types of programmable shader code, including shader
program code to implement vertex shaders, fragment shaders, and/or
compute shaders. The exact number of shader cores present can vary
among embodiments and implementations. Additionally, graphics
processor 1340 includes an inter-core task manager 1345, which acts
as a thread dispatcher to dispatch execution threads to one or more
shader cores 1355A-1355N and a tiling unit 1358 to accelerate
tiling operations for tile-based rendering, in which rendering
operations for a scene are subdivided in image space, for example
to exploit local spatial coherence within a scene or to optimize
use of internal caches.
Ray Tracing with Machine Learning
[0270] As mentioned above, ray tracing is a graphics processing
technique in which a light transport is simulated through
physically-based rendering. One of the key operations in ray
tracing is processing a visibility query which requires traversal
and intersection testing of nodes in a bounding volume hierarchy
(BVH).
[0271] Ray- and path-tracing based techniques compute images by
tracing rays and paths through each pixel, and using random
sampling to compute advanced effects such as shadows, glossiness,
indirect illumination, etc. Using only a few samples is fast but
produces noisy images while using many samples produces high
quality images, but is cost prohibitive.
[0272] Machine learning includes any circuitry, program code, or
combination thereof capable of progressively improving performance
of a specified task or rendering progressively more accurate
predictions or decisions. Some machine learning engines can perform
these tasks or render these predictions/decisions without being
explicitly programmed to perform the tasks or render the
predictions/decisions. A variety of machine learning techniques
exist including (but not limited to) supervised and semi-supervised
learning, unsupervised learning, and reinforcement learning.
[0273] In the last several years, a breakthrough solution to
ray-/path-tracing for real-time use has come in the form of
"denoising"--the process of using image processing techniques to
produce high quality, filtered/denoised images from noisy,
low-sample count inputs. The most effective denoising techniques
rely on machine learning techniques where a machine-learning engine
learns what a noisy image would likely look like if it had been
computed with more samples. In one particular implementation, the
machine learning is performed by a convolutional neural network
(CNN); however, the underlying principles of the invention are not
limited to a CNN implementation. In such an implementation,
training data is produced with low-sample count inputs and
ground-truth. The CNN is trained to predict the converged pixel
from a neighborhood of noisy pixel inputs around the pixel in
question.
[0274] Though not perfect, this AI-based denoising technique has
proven surprisingly effective. The caveat, however, is that good
training data is required, since the network may otherwise predict
the wrong results. For example, if an animated movie studio trained
a denoising CNN on past movies with scenes on land and then
attempted to use the trained CNN to denoise frames from a new movie
set on water, the denoising operation will perform
sub-optimally.
[0275] To address this problem, learning data can be dynamically
gathered, while rendering, and a machine learning engine, such as a
CNN, may be continuously trained based on the data on which it is
currently being run, thus continuously improving the machine
learning engine for the task at hand. Therefore, a training phase
may still performed prior to runtime, but continued to adjust the
machine learning weights as needed during runtime. Thereby, the
high cost of computing the reference data required for the training
is avoided by restricting the generation of learning data to a
sub-region of the image every frame or every N frames. In
particular, the noisy inputs of a frame are generated for denoising
the full frame with the current network. In addition, a small
region of reference pixels are generated and used for continuous
training, as described below.
[0276] While a CNN implementation is described herein, any form of
machine learning engine may be used including, but not limited to
systems which perform supervised learning (e.g., building a
mathematical model of a set of data that contains both the inputs
and the desired outputs), unsupervised learning (e.g., which
evaluate the input data for certain types of structure), and/or a
combination of supervised and unsupervised learning.
[0277] Existing de-noising implementations operate in a training
phase and a runtime phase. During the training phase, a network
topology is defined which receives a region of N.times.N pixels
with various per-pixel data channels such as pixel color, depth,
normal, normal deviation, primitive IDs, and albedo and generates a
final pixel color. A set of "representative" training data is
generated using one frame's worth of low-sample count inputs, and
referencing the "desired" pixel colors computed with a very high
sample count. The network is trained towards these inputs,
generating a set of "ideal" weights for the network. In these
implementations, the reference data is used to train the network's
weights to most closely match the network's output to the desired
result.
[0278] At runtime, the given, pre-computed ideal network weights
are loaded and the network is initialized. For each frame, a
low-sample count image of denoising inputs (i.e., the same as used
for training) is generated. For each pixel, the given neighborhood
of pixels' inputs is run through the network to predict the
"denoised" pixel color, generating a denoised frame.
[0279] FIG. 15 illustrates an initial training implementation. A
machine learning engine 1500 (e.g., a CNN) receives a region of
N.times.N pixels as high sample count image data 1702 with various
per-pixel data channels such as pixel color, depth, normal, normal
deviation, primitive IDs, and albedo and generates final pixel
colors. Representative training data is generated using one frame's
worth of low-sample count inputs 1501. The network is trained
towards these inputs, generating a set of "ideal" weights 1505
which the machine learning engine 1500 subsequently uses to denoise
low sample count images at runtime.
[0280] To improve the above techniques, the denoising phase to
generate new training data every frame or a subset of frames (e.g.,
every N frames where N=2, 3, 4, 10, 25, etc) is augmented. In
particular, as illustrated in FIG. 16, one or more regions in each
frame are chosen, referred to here as "new reference regions" 1602
which are rendered with a high sample count into a separate high
sample count buffer 1604. A low sample count buffer 1603 stores the
low sample count input frame 1601 (including the low sample region
1604 corresponding to the new reference region 1602).
[0281] The location of the new reference region 1602 may be
randomly selected. Alternatively, the location of the new reference
region 1602 may be adjusted in a pre-specified manner for each new
frame (e.g., using a predefined movement of the region between
frames, limited to a specified region in the center of the frame,
etc).
[0282] Regardless of how the new reference region is selected, it
is used by the machine learning engine 1600 to continually refine
and update the trained weights 1605 used for denoising. In
particular, reference pixel colors from each new reference region
1602 and noisy reference pixel inputs from a corresponding low
sample count region 1607 are rendered. Supplemental training is
then performed on the machine learning engine 1600 using the
high-sample-count reference region 1602 and the corresponding low
sample count region 1607. In contrast to the initial training, this
training is performed continuously during runtime for each new
reference region 1602--thereby ensuring that the machine learning
engine 1600 is precisely trained. For example, per-pixel data
channels (e.g., pixel color, depth, normal, normal deviation, etc)
may be evaluated, which the machine learning engine 1600 uses to
make adjustments to the trained weights 1605. As in the training
case (FIG. 15), the machine learning engine 1600 is trained towards
a set of ideal weights 1605 for removing noise from the low sample
count input frame 1601 to generate the denoised frame 1620.
However, the trained weights 1605 are continually updated, based on
new image characteristics of new types of low sample count input
frames 1601.
[0283] The re-training operations performed by the machine learning
engine 1600 may be executed concurrently in a background process on
the graphics processor unit (GPU) or host processor. The render
loop, which may be implemented as a driver component and/or a GPU
hardware component, may continuously produce new training data
(e.g., in the form of new reference regions 1602) which it places
in a queue. The background training process, executed on the GPU or
host processor, may continuously read the new training data from
this queue, re-trains the machine learning engine 1600, and update
it with new weights 1605 at appropriate intervals.
[0284] FIG. 17 illustrates an example of one such implementation in
which the background training process 1700 is implemented by the
host CPU 1710. In particular, the background training process 1700
uses the high sample count new reference region 1602 and the
corresponding low sample region 1604 to continually update the
trained weights 1605, thereby updating the machine learning engine
1600.
[0285] As illustrated in FIG. 18A for the non-limiting example of a
multi-player online game, different host machines 1820-1822
individually generate reference regions which a background training
process 1700A-C transmits to a server 1800 (e.g., such as a gaming
server). The server 1800 then performs training on a machine
learning engine 1810 using the new reference regions received from
each of the hosts 1821-1822, updating the weights 1805 as
previously described. It transmits these weights 1805 to the host
machines 1820 which store the weights 1605A-C, thereby updating
each individual machine learning engine (not shown). Because the
server 1800 may be provided a large number of reference regions in
a short period of time, it can efficiently and precisely update the
weights for any given application (e.g., an online game) being
executed by the users.
[0286] As illustrated in FIG. 18B, the different host machines may
generate new trained weights (e.g., based on training/reference
regions 1602 as previously described) and share the new trained
weights with a server 1800 (e.g., such as a gaming server) or,
alternatively, use a peer-to-peer sharing protocol. A machine
learning management component 1810 on the server generates a set of
combined weights 1805 using the new weights received from each of
the host machines. The combined weights 1805, for example, may be
an average generated from the new weights and continually updated
as described herein. Once generated, copies of the combined weights
1605A-C may be transmitted and stored on each of the host machines
1820-1821 which may then use the combined weights as described
herein to perform de-noising operations.
[0287] The semi-closed loop update mechanism can also be used by
the hardware manufacturer. For example, the reference network may
be included as part of the driver distributed by the hardware
manufacturer. As the driver generates new training data using the
techniques described herein and continuously submits these back to
the hardware manufacturer, the hardware manufacturer uses this
information to continue to improve its machine learning
implementations for the next driver update.
[0288] In an example implementation (e.g., in batch movie rendering
on a render farm), the renderer transmits the newly generated
training regions to a dedicated server or database (in that
studio's render farm) that aggregates this data from multiple
render nodes over time. A separate process on a separate machine
continuously improves the studio's dedicated denoising network, and
new render jobs always use the latest trained network.
[0289] A machine-learning method is illustrated in FIG. 19. The
method may be implemented on the architectures described herein,
but is not limited to any particular system or graphics processing
architecture.
[0290] At 1901, as part of the initial training phase, low sample
count image data and high sample count image data are generated for
a plurality of image frames. At 1902, a machine-learning denoising
engine is trained using the high/low sample count image data. For
example, a set of convolutional neural network weights associated
with pixel features may be updated in accordance with the training.
However, any machine-learning architecture may be used.
[0291] At 1903, at runtime, low sample count image frames are
generated along with at least one reference region having a high
sample count. At 1904, the high sample count reference region is
used by the machine-learning engine and/or separate training logic
(e.g., background training module 1700) to continually refine the
training of the machine learning engine. For example, the high
sample count reference region may be used in combination with a
corresponding portion of the low sample count image to continue to
teach the machine learning engine 1904 how to most effectively
perform denoising. In a CNN implementation, for example, this may
involve updating the weights associated with the CNN.
[0292] Multiple variations described above may be implemented, such
as the manner in which the feedback loop to the machine learning
engine is configured, the entities which generate the training
data, the manner in which the training data is fed back to training
engine, and how the improved network is provided to the rendering
engines. In addition, while the examples described above perform
continuous training using a single reference region, any number of
reference regions may be used. Moreover, as previously mentioned,
the reference regions may be of different sizes, may be used on
different numbers of image frames, and may be positioned in
different locations within the image frames using different
techniques (e.g., random, according to a predetermined pattern,
etc).
[0293] In addition, while a convolutional neural network (CNN) is
described as one example of a machine-learning engine 1600, the
underlying principles of the invention may be implemented using any
form of machine learning engine which is capable of continually
refining its results using new training data. By way of example,
and not limitation, other machine learning implementations include
the group method of data handling (GMDH), long short-term memory,
deep reservoir computing, deep belief networks, tensor deep
stacking networks, and deep predictive coding networks, to name a
few.
Apparatus and Method for Efficient Distributed Denoising
[0294] As described above, denoising has become a critical feature
for real-time ray tracing with smooth, noiseless images. Rendering
can be done across a distributed system on multiple devices, but so
far the existing denoising frameworks all operate on a single
instance on a single machine. If rendering is being done across
multiple devices, they may not have all rendered pixels accessible
for computing a denoised portion of the image.
[0295] A distributed denoising algorithm that works with both
artificial intelligence (AI) and non-AI based denoising techniques
is presented. Regions of the image are either already distributed
across nodes from a distributed render operation, or split up and
distributed from a single framebuffer. Ghost regions of neighboring
regions needed for computing sufficient denoising are collected
from neighboring nodes when needed, and the final resulting tiles
are composited into a final image.
Distributed Processing
[0296] FIG. 20 illustrates multiple nodes 2021-2023 that perform
rendering. While only three nodes are illustrated for simplicity,
the underlying principles of the invention are not limited to any
particular number of nodes. In fact, a single node may be used to
implement certain embodiments of the invention.
[0297] Nodes 2021-2023 each render a portion of an image, resulting
in regions 2011-2013 in this example. While rectangular regions
2011-2013 are shown in FIG. 20, regions of any shape may be used
and any device can process any number of regions. The regions that
are needed by a node to perform a sufficiently smooth denoising
operation are referred to as ghost regions 2011-2013. In other
words, the ghost regions 2001-2003 represent the entirety of data
required to perform denoising at a specified level of quality.
Lowering the quality level reduces the size of the ghost region and
therefore the amount of data required and raising the quality level
increases the ghost region and corresponding data required.
[0298] If a node such as node 2021 does have a local copy of a
portion of the ghost region 2001 required to denoise its region
2011 at a specified level of quality, the node will retrieve the
required data from one or more "adjacent" nodes, such as node 2022
which owns a portion of ghost region 2001 as illustrated.
Similarly, if node 2022 does have a local copy of a portion of
ghost region 2002 required to denoise its region 2012 at the
specified level of quality, node 2022 will retrieve the required
ghost region data 2032 from node 2021. The retrieval may be
performed over a bus, an interconnect, a high speed memory fabric,
a network (e.g., high speed Ethernet), or may even be an on-chip
interconnect in a multi-core chip capable of distributing rendering
work among a plurality of cores (e.g., used for rendering large
images at either extreme resolutions or time varying). Each node
2021-2023 may comprise an individual execution unit or specified
set of execution units within a graphics processor.
[0299] The specific amount of data to be sent is dependent on the
denoising techniques being used. Moreover, the data from the ghost
region may include any data needed to improve denoising of each
respective region. For example, the ghost region data may include
image colors/wavelengths, intensity/alpha data, and/or normals.
However, the underlying principles of the invention are not limited
to any particular set of ghost region data.
Additional Details
[0300] For slower networks or interconnects, compression of this
data can be utilized using existing general purpose lossless or
lossy compression. Examples include, but are not limited to, zlib,
gzip, and Lempel-Ziv-Markov chain algorithm (LZMA). Further
content-specific compression may be used by noting that the delta
in ray hit information between frames can be quite sparse, and only
the samples that contribute to that delta need to be sent when the
node already has the collected deltas from previous frames. These
can be selectively pushed to nodes that collect those samples, i,
or node i can request samples from other nodes. Lossless
compression is used for certain types of data and program code
while lossy data is used for other types of data.
[0301] FIG. 21 illustrates additional details of the interactions
between nodes 2021-2022. Each node 2021-2022 includes a ray tracing
rendering circuitry 2081-2082 for rendering the respective image
regions 2011-2012 and ghost regions 2001-2002. Denoisers 2100-2111
execute denoising operations on the regions 2011-2012,
respectively, which each node 2021-2022 is responsible for
rendering and denoising. The denoisers 2021-2022, for example, may
comprise circuitry, software, or any combination thereof to
generate the denoised regions 2121-2122, respectively. As
mentioned, when generating denoised regions the denoisers 2021-2022
may need to rely on data within a ghost region owned by a different
node (e.g., denoiser 2100 may need data from ghost region 2002
owned by node 2022).
[0302] Thus, the denoisers 2100-2111 may generate the denoised
regions 2121-2122 using data from regions 2011-2012 and ghost
regions 2001-2002, respectively, at least a portion of which may be
received from another node. Region data managers 2101-2102 may
manage data transfers from ghost regions 2001-2002 as described
herein.
[0303] Compressor/decompressor units 2131-2132 may perform
compression and decompression of the ghost region data exchanged
between the nodes 2021-2022, respectively.
[0304] For example, region data manager 2101 of node 2021 may, upon
request from node 2022, send data from ghost region 2001 to
compressor/decompressor 2131, which compresses the data to generate
compressed data 2106 which it transmits to node 2022, thereby
reducing bandwidth over the interconnect, network, bus, or other
data communication link. Compressor/decompressor 2132 of node 2022
then decompresses the compressed data 2106 and denoiser 2111 uses
the decompressed ghost data to generate a higher quality denoised
region 2012 than would be possible with only data from region 2012.
The region data manager 2102 may store the decompressed data from
ghost region 2001 in a cache, memory, register file or other
storage to make it available to the denoiser 2111 when generating
the denoised region 2122. A similar set of operations may be
performed to provide the data from ghost region 2002 to denoiser
2100 on node 2021 which uses the data in combination with data from
region 2011 to generate a higher quality denoised region 2121.
Grab Data or Render
[0305] If the connection between devices such as nodes 2021-2022 is
slow (i.e., lower than a threshold latency and/or threshold
bandwidth), it may be faster to render ghost regions locally rather
than requesting the results from other devices. This can be
determined at run-time by tracking network transaction speeds and
linearly extrapolated render times for the ghost region size. In
such cases where it is faster to render out the entire ghost
region, multiple devices may end up rendering the same portions of
the image. The resolution of the rendered portion of the ghost
regions may be adjusted based on the variance of the base region
and the determined degree of blurring.
Load Balancing
[0306] Static and/or dynamic load balancing schemes may be used to
distribute the processing load among the various nodes 2021-2023.
For dynamic load balancing, the variance determined by the
denoising filter may require both more time in denoising but drive
the amount of samples used to render a particular region of the
scene, with low variance and blurry regions of the image requiring
fewer samples. The specific regions assigned to specific nodes may
be adjusted dynamically based on data from previous frames or
dynamically communicated across devices as they are rendering so
that all devices will have the same amount of work.
[0307] FIG. 22 illustrates how a monitor 2201-2202 running on each
respective node 2021-2022 collects performance metric data
including, but not limited to, the time consumed to transmit data
over the network interface 2211-2212, the time consumed when
denoising a region (with and without ghost region data), and the
time consumed rendering each region/ghost region. The monitors
2201-2202 report these performance metrics back to a manager or
load balancer node 2201, which analyzes the data to identify the
current workload on each node 2021-2022 and potentially determines
a more efficient mode of processing the various denoised regions
2121-2122. The manager node 2201 then distributes new workloads for
new regions to the nodes 2021-2022 in accordance with the detected
load. For example, the manager node 2201 may transmit more work to
those nodes which are not heavily loaded and/or reallocate work
from those nodes which are overloaded. In addition, the load
balancer node 2201 may transmit a reconfiguration command to adjust
the specific manner in which rendering and/or denoising is
performed by each of the nodes (some examples of which are
described above).
Determining Ghost Regions
[0308] The sizes and shapes of the ghost regions 2001-2002 may be
determined based on the denoising algorithm implemented by the
denoisers 2100-2111. Their respective sizes can then be dynamically
modified based on the detected variance of the samples being
denoised. The learning algorithm used for AI denoising itself may
be used for determining appropriate region sizes, or in other cases
such as a bilateral blur the predetermined filter width will
determine the size of the ghost regions 2001-2002. In an exemplary
implementation which uses a learning algorithm, the machine
learning engine may be executed on the manager node 2201 and/or
portions of the machine learning may be executed on each of the
individual nodes 2021-2023 (see, e.g., FIGS. 18A-B and associated
text above).
Gathering the Final Image
[0309] The final image may be generated by gathering the rendered
and denoised regions from each of the nodes 2021-2023, without the
need for the ghost regions or normals. In FIG. 22, for example, the
denoised regions 2121-2122 are transmitted to regions processor
2280 of the manager node 2201 which combines the regions to
generate the final denoised image 2290, which is then displayed on
a display 2290. The region processor 2280 may combine the regions
using a variety of 2D compositing techniques. Although illustrated
as separate components, the region processor 2280 and denoised
image 2290 may be integral to the display 2290. The various nodes
2021-2022 may use a direct-send technique to transmit the denoised
regions 2121-2122 and potentially using various lossy or lossless
compression of the region data.
[0310] AI denoising is still a costly operation and as gaming moves
into the cloud. As such, distributing processing of denoising
across multiple nodes 2021-2022 may become required for achieving
real-time frame rates for traditional gaming or virtual reality
(VR) which requires higher frame rates. Movie studios also often
render in large render farms which can be utilized for faster
denoising.
[0311] An exemplary method for performing distributed rendering and
denoising is illustrated in FIG. 23. The method may be implemented
within the context of the system architectures described above, but
is not limited to any particular system architecture.
[0312] At 2301, graphics work is dispatched to a plurality of nodes
which perform ray tracing operations to render a region of an image
frame. Each node may already have data required to perform the
operations in memory. For example, two or more of the nodes may
share a common memory or the local memories of the nodes may
already have stored data from prior ray tracing operations.
Alternatively, or in addition, certain data may be transmitted to
each node.
[0313] At 2302, the "ghost region" required for a specified level
of denoising (i.e., at an acceptable level of performance) is
determined. The ghost region comprises any data required to perform
the specified level of denoising, including data owned by one or
more other nodes.
[0314] At 2303, data related to the ghost regions (or portions
thereof) is exchanged between nodes. At 2304 each node performs
denoising on its respective region (e.g., using the exchanged data)
and at 2305 the results are combined to generate the final denoised
image frame.
[0315] A manager node or primary node such as shown in FIG. 22 may
dispatched the work to the nodes and then combine the work
performed by the nodes to generate the final image frame. A
peer-based architecture can be used where the nodes are peers which
exchange data to render and denoise the final image frame.
[0316] The nodes described herein (e.g., nodes 2021-2023) may be
graphics processing computing systems interconnected via a high
speed network. Alternatively, the nodes may be individual
processing elements coupled to a high speed memory fabric. All of
the nodes may share a common virtual memory space and/or a common
physical memory. Alternatively, the nodes may be a combination of
CPUs and GPUs. For example, the manager node 2201 described above
may be a CPU and/or software executed on the CPU and the nodes
2021-2022 may be GPUs and/or software executed on the GPUs. Various
different types of nodes may be used while still complying with the
underlying principles of the invention.
Example Neural Network Implementations
[0317] There are many types of neural networks; a simple type of
neural network is a feedforward network. A feedforward network may
be implemented as an acyclic graph in which the nodes are arranged
in layers. Typically, a feedforward network topology includes an
input layer and an output layer that are separated by at least one
hidden layer. The hidden layer transforms input received by the
input layer into a representation that is useful for generating
output in the output layer. The network nodes are fully connected
via edges to the nodes in adjacent layers, but there are no edges
between nodes within each layer. Data received at the nodes of an
input layer of a feedforward network are propagated (i.e., "fed
forward") to the nodes of the output layer via an activation
function that calculates the states of the nodes of each successive
layer in the network based on coefficients ("weights") respectively
associated with each of the edges connecting the layers. Depending
on the specific model being represented by the algorithm being
executed, the output from the neural network algorithm can take
various forms.
[0318] Before a machine learning algorithm can be used to model a
particular problem, the algorithm is trained using a training data
set. Training a neural network involves selecting a network
topology, using a set of training data representing a problem being
modeled by the network, and adjusting the weights until the network
model performs with a minimal error for all instances of the
training data set. For example, during a supervised learning
training process for a neural network, the output produced by the
network in response to the input representing an instance in a
training data set is compared to the "correct" labeled output for
that instance, an error signal representing the difference between
the output and the labeled output is calculated, and the weights
associated with the connections are adjusted to minimize that error
as the error signal is backward propagated through the layers of
the network. The network is considered "trained" when the errors
for each of the outputs generated from the instances of the
training data set are minimized.
[0319] The accuracy of a machine learning algorithm can be affected
significantly by the quality of the data set used to train the
algorithm. The training process can be computationally intensive
and may require a significant amount of time on a conventional
general-purpose processor. Accordingly, parallel processing
hardware is used to train many types of machine learning
algorithms. This is particularly useful for optimizing the training
of neural networks, as the computations performed in adjusting the
coefficients in neural networks lend themselves naturally to
parallel implementations. Specifically, many machine learning
algorithms and software applications have been adapted to make use
of the parallel processing hardware within general-purpose graphics
processing devices.
[0320] FIG. 24 is a generalized diagram of a machine learning
software stack 2400. A machine learning application 2402 can be
configured to train a neural network using a training dataset or to
use a trained deep neural network to implement machine
intelligence. The machine learning application 2402 can include
training and inference functionality for a neural network and/or
specialized software that can be used to train a neural network
before deployment. The machine learning application 2402 can
implement any type of machine intelligence including but not
limited to image recognition, mapping and localization, autonomous
navigation, speech synthesis, medical imaging, or language
translation.
[0321] Hardware acceleration for the machine learning application
2402 can be enabled via a machine learning framework 2404. The
machine learning framework 2404 may be implemented on hardware
described herein, such as the processing system 100 comprising the
processors and components described herein. The elements described
for FIG. 24 having the same or similar names as the elements of any
other figure herein describe the same elements as in the other
figures, can operate or function in a manner similar to that, can
comprise the same components, and can be linked to other entities,
as those described elsewhere herein, but are not limited to such.
The machine learning framework 2404 can provide a library of
machine learning primitives. Machine learning primitives are basic
operations that are commonly performed by machine learning
algorithms. Without the machine learning framework 2404, developers
of machine learning algorithms would be required to create and
optimize the main computational logic associated with the machine
learning algorithm, then re-optimize the computational logic as new
parallel processors are developed. Instead, the machine learning
application can be configured to perform the necessary computations
using the primitives provided by the machine learning framework
2404. Exemplary primitives include tensor convolutions, activation
functions, and pooling, which are computational operations that are
performed while training a convolutional neural network (CNN). The
machine learning framework 2404 can also provide primitives to
implement basic linear algebra subprograms performed by many
machine-learning algorithms, such as matrix and vector
operations.
[0322] The machine learning framework 2404 can process input data
received from the machine learning application 2402 and generate
the appropriate input to a compute framework 2406. The compute
framework 2406 can abstract the underlying instructions provided to
the GPGPU driver 2408 to enable the machine learning framework 2404
to take advantage of hardware acceleration via the GPGPU hardware
2410 without requiring the machine learning framework 2404 to have
intimate knowledge of the architecture of the GPGPU hardware 2410.
Additionally, the compute framework 2406 can enable hardware
acceleration for the machine learning framework 2404 across a
variety of types and generations of the GPGPU hardware 2410.
[0323] GPGPU Machine Learning Acceleration
[0324] FIG. 25 illustrates a multi-GPU computing system 2500, which
may be a variant of the processing system 100. Therefore, the
disclosure of any features in combination with the processing
system 100 herein also discloses a corresponding combination with
multi-GPU computing system 2500, but is not limited to such. The
elements of FIG. 25 having the same or similar names as the
elements of any other figure herein describe the same elements as
in the other figures, can operate or function in a manner similar
to that, can comprise the same components, and can be linked to
other entities, as those described elsewhere herein, but are not
limited to such. The multi-GPU computing system 2500 can include a
processor 2502 coupled to multiple GPGPUs 2506A-D via a host
interface switch 2504. The host interface switch 2504 may for
example be a PCI express switch device that couples the processor
2502 to a PCI express bus over which the processor 2502 can
communicate with the set of GPGPUs 2506A-D. Each of the multiple
GPGPUs 2506A-D can be an instance of the GPGPU described above. The
GPGPUs 2506A-D can interconnect via a set of high-speed point to
point GPU to GPU links 2516. The high-speed GPU to GPU links can
connect to each of the GPGPUs 2506A-D via a dedicated GPU link. The
P2P GPU links 2516 enable direct communication between each of the
GPGPUs 2506A-D without requiring communication over the host
interface bus to which the processor 2502 is connected. With
GPU-to-GPU traffic directed to the P2P GPU links, the host
interface bus remains available for system memory access or to
communicate with other instances of the multi-GPU computing system
2500, for example, via one or more network devices. Instead of
connecting the GPGPUs 2506A-D to the processor 2502 via the host
interface switch 2504, the processor 2502 can include direct
support for the P2P GPU links 2516 and, thus, connect directly to
the GPGPUs 2506A-D.
[0325] Machine Learning Neural Network Implementations
[0326] The computing architecture described herein can be
configured to perform the types of parallel processing that is
particularly suited for training and deploying neural networks for
machine learning. A neural network can be generalized as a network
of functions having a graph relationship. As is well-known in the
art, there are a variety of types of neural network implementations
used in machine learning. One exemplary type of neural network is
the feedforward network, as previously described.
[0327] A second exemplary type of neural network is the
Convolutional Neural Network (CNN). A CNN is a specialized
feedforward neural network for processing data having a known,
grid-like topology, such as image data. Accordingly, CNNs are
commonly used for compute vision and image recognition
applications, but they also may be used for other types of pattern
recognition such as speech and language processing. The nodes in
the CNN input layer are organized into a set of "filters" (feature
detectors inspired by the receptive fields found in the retina),
and the output of each set of filters is propagated to nodes in
successive layers of the network. The computations for a CNN
include applying the convolution mathematical operation to each
filter to produce the output of that filter. Convolution is a
specialized kind of mathematical operation performed by two
functions to produce a third function that is a modified version of
one of the two original functions. In convolutional network
terminology, the first function to the convolution can be referred
to as the input, while the second function can be referred to as
the convolution kernel. The output may be referred to as the
feature map. For example, the input to a convolution layer can be a
multidimensional array of data that defines the various color
components of an input image. The convolution kernel can be a
multidimensional array of parameters, where the parameters are
adapted by the training process for the neural network.
[0328] Recurrent neural networks (RNNs) are a family of feedforward
neural networks that include feedback connections between layers.
RNNs enable modeling of sequential data by sharing parameter data
across different parts of the neural network. The architecture for
a RNN includes cycles. The cycles represent the influence of a
present value of a variable on its own value at a future time, as
at least a portion of the output data from the RNN is used as
feedback for processing subsequent input in a sequence. This
feature makes RNNs particularly useful for language processing due
to the variable nature in which language data can be composed.
[0329] The figures described below present exemplary feedforward,
CNN, and RNN networks, as well as describe a general process for
respectively training and deploying each of those types of
networks. It will be understood that these descriptions are
exemplary and non-limiting and the concepts illustrated can be
applied generally to deep neural networks and machine learning
techniques in general.
[0330] The exemplary neural networks described above can be used to
perform deep learning. Deep learning is machine learning using deep
neural networks. The deep neural networks used in deep learning are
artificial neural networks composed of multiple hidden layers, as
opposed to shallow neural networks that include only a single
hidden layer. Deeper neural networks are generally more
computationally intensive to train. However, the additional hidden
layers of the network enable multistep pattern recognition that
results in reduced output error relative to shallow machine
learning techniques.
[0331] Deep neural networks used in deep learning typically include
a front-end network to perform feature recognition coupled to a
back-end network which represents a mathematical model that can
perform operations (e.g., object classification, speech
recognition, etc.) based on the feature representation provided to
the model. Deep learning enables machine learning to be performed
without requiring hand crafted feature engineering to be performed
for the model. Instead, deep neural networks can learn features
based on statistical structure or correlation within the input
data. The learned features can be provided to a mathematical model
that can map detected features to an output. The mathematical model
used by the network is generally specialized for the specific task
to be performed, and different models will be used to perform
different task.
[0332] Once the neural network is structured, a learning model can
be applied to the network to train the network to perform specific
tasks. The learning model describes how to adjust the weights
within the model to reduce the output error of the network.
Backpropagation of errors is a common method used to train neural
networks. An input vector is presented to the network for
processing. The output of the network is compared to the desired
output using a loss function and an error value is calculated for
each of the neurons in the output layer. The error values are then
propagated backwards until each neuron has an associated error
value which roughly represents its contribution to the original
output. The network can then learn from those errors using an
algorithm, such as the stochastic gradient descent algorithm, to
update the weights of the of the neural network.
[0333] FIGS. 26-27 illustrate an exemplary convolutional neural
network. FIG. 26 illustrates various layers within a CNN. As shown
in FIG. 26, an exemplary CNN used to model image processing can
receive input 2602 describing the red, green, and blue (RGB)
components of an input image. The input 2602 can be processed by
multiple convolutional layers (e.g., convolutional layer 2604,
convolutional layer 2606). The output from the multiple
convolutional layers may optionally be processed by a set of fully
connected layers 2608. Neurons in a fully connected layer have full
connections to all activations in the previous layer, as previously
described for a feedforward network. The output from the fully
connected layers 2608 can be used to generate an output result from
the network. The activations within the fully connected layers 2608
can be computed using matrix multiplication instead of convolution.
Not all CNN implementations make use of fully connected layers. For
example, in some implementations the convolutional layer 2606 can
generate output for the CNN.
[0334] The convolutional layers are sparsely connected, which
differs from traditional neural network configuration found in the
fully connected layers 2608. Traditional neural network layers are
fully connected, such that every output unit interacts with every
input unit. However, the convolutional layers are sparsely
connected because the output of the convolution of a field is input
(instead of the respective state value of each of the nodes in the
field) to the nodes of the subsequent layer, as illustrated. The
kernels associated with the convolutional layers perform
convolution operations, the output of which is sent to the next
layer. The dimensionality reduction performed within the
convolutional layers is one aspect that enables the CNN to scale to
process large images.
[0335] FIG. 27 illustrates exemplary computation stages within a
convolutional layer of a CNN. Input to a convolutional layer 2712
of a CNN can be processed in three stages of a convolutional layer
2714. The three stages can include a convolution stage 2716, a
detector stage 2718, and a pooling stage 2720. The convolution
layer 2714 can then output data to a successive convolutional
layer. The final convolutional layer of the network can generate
output feature map data or provide input to a fully connected
layer, for example, to generate a classification value for the
input to the CNN.
[0336] In the convolution stage 2716 performs several convolutions
in parallel to produce a set of linear activations. The convolution
stage 2716 can include an affine transformation, which is any
transformation that can be specified as a linear transformation
plus a translation. Affine transformations include rotations,
translations, scaling, and combinations of these transformations.
The convolution stage computes the output of functions (e.g.,
neurons) that are connected to specific regions in the input, which
can be determined as the local region associated with the neuron.
The neurons compute a dot product between the weights of the
neurons and the region in the local input to which the neurons are
connected. The output from the convolution stage 2716 defines a set
of linear activations that are processed by successive stages of
the convolutional layer 2714.
[0337] The linear activations can be processed by a detector stage
2718. In the detector stage 2718, each linear activation is
processed by a non-linear activation function. The non-linear
activation function increases the nonlinear properties of the
overall network without affecting the receptive fields of the
convolution layer. Several types of non-linear activation functions
may be used. One particular type is the rectified linear unit
(ReLU), which uses an activation function defined as f(x)=max
(0,x), such that the activation is thresholded at zero.
[0338] The pooling stage 2720 uses a pooling function that replaces
the output of the convolutional layer 2706 with a summary statistic
of the nearby outputs. The pooling function can be used to
introduce translation invariance into the neural network, such that
small translations to the input do not change the pooled outputs.
Invariance to local translation can be useful in scenarios where
the presence of a feature in the input data is more important than
the precise location of the feature. Various types of pooling
functions can be used during the pooling stage 2720, including max
pooling, average pooling, and I2-norm pooling. Additionally, some
CNN implementations do not include a pooling stage. Instead, such
implementations substitute and additional convolution stage having
an increased stride relative to previous convolution stages.
[0339] The output from the convolutional layer 2714 can then be
processed by the next layer 2722. The next layer 2722 can be an
additional convolutional layer or one of the fully connected layers
2708. For example, the first convolutional layer 2704 of FIG. 27
can output to the second convolutional layer 2706, while the second
convolutional layer can output to a first layer of the fully
connected layers 2808.
[0340] FIG. 28 illustrates an exemplary recurrent neural network
2800. In a recurrent neural network (RNN), the previous state of
the network influences the output of the current state of the
network. RNNs can be built in a variety of ways using a variety of
functions. The use of RNNs generally revolves around using
mathematical models to predict the future based on a prior sequence
of inputs. For example, an RNN may be used to perform statistical
language modeling to predict an upcoming word given a previous
sequence of words. The illustrated RNN 2800 can be described has
having an input layer 2802 that receives an input vector, hidden
layers 2804 to implement a recurrent function, a feedback mechanism
2805 to enable a `memory` of previous states, and an output layer
2806 to output a result. The RNN 2800 operates based on time-steps.
The state of the RNN at a given time step is influenced based on
the previous time step via the feedback mechanism 2805. For a given
time step, the state of the hidden layers 2804 is defined by the
previous state and the input at the current time step. An initial
input (x1) at a first time step can be processed by the hidden
layer 2804. A second input (x2) can be processed by the hidden
layer 2804 using state information that is determined during the
processing of the initial input (x1). A given state can be computed
as s_t=f(Ux_t+Ws_(t-1)), where U and W are parameter matrices. The
function f is generally a nonlinearity, such as the hyperbolic
tangent function (Tan h) or a variant of the rectifier function
f(x)=max (0,x). However, the specific mathematical function used in
the hidden layers 2804 can vary depending on the specific
implementation details of the RNN 2800.
[0341] In addition to the basic CNN and RNN networks described,
variations on those networks may be enabled. One example RNN
variant is the long short term memory (LSTM) RNN. LSTM RNNs are
capable of learning long-term dependencies that may be necessary
for processing longer sequences of language. A variant on the CNN
is a convolutional deep belief network, which has a structure
similar to a CNN and is trained in a manner similar to a deep
belief network. A deep belief network (DBN) is a generative neural
network that is composed of multiple layers of stochastic (random)
variables. DBNs can be trained layer-by-layer using greedy
unsupervised learning. The learned weights of the DBN can then be
used to provide pre-train neural networks by determining an optimal
initial set of weights for the neural network.
[0342] FIG. 29 illustrates training and deployment of a deep neural
network. Once a given network has been structured for a task the
neural network is trained using a training dataset 2902. Various
training frameworks 2904 have been developed to enable hardware
acceleration of the training process. For example, the machine
learning framework described above may be configured as a training
framework. The training framework 2904 can hook into an untrained
neural network 2906 and enable the untrained neural net to be
trained using the parallel processing resources described herein to
generate a trained neural net 2908.
[0343] To start the training process the initial weights may be
chosen randomly or by pre-training using a deep belief network. The
training cycle then be performed in either a supervised or
unsupervised manner.
[0344] Supervised learning is a learning method in which training
is performed as a mediated operation, such as when the training
dataset 2902 includes input paired with the desired output for the
input, or where the training dataset includes input having known
output and the output of the neural network is manually graded. The
network processes the inputs and compares the resulting outputs
against a set of expected or desired outputs. Errors are then
propagated back through the system. The training framework 2904 can
adjust to adjust the weights that control the untrained neural
network 2906. The training framework 2904 can provide tools to
monitor how well the untrained neural network 2906 is converging
towards a model suitable to generating correct answers based on
known input data. The training process occurs repeatedly as the
weights of the network are adjusted to refine the output generated
by the neural network. The training process can continue until the
neural network reaches a statistically desired accuracy associated
with a trained neural net 2908. The trained neural network 2908 can
then be deployed to implement any number of machine learning
operations.
[0345] Unsupervised learning is a learning method in which the
network attempts to train itself using unlabeled data. Thus, for
unsupervised learning the training dataset 2902 will include input
data without any associated output data. The untrained neural
network 2906 can learn groupings within the unlabeled input and can
determine how individual inputs are related to the overall dataset.
Unsupervised training can be used to generate a self-organizing
map, which is a type of trained neural network 2907 capable of
performing operations useful in reducing the dimensionality of
data. Unsupervised training can also be used to perform anomaly
detection, which allows the identification of data points in an
input dataset that deviate from the normal patterns of the
data.
[0346] Variations on supervised and unsupervised training may also
be employed. Semi-supervised learning is a technique in which in
the training dataset 2902 includes a mix of labeled and unlabeled
data of the same distribution. Incremental learning is a variant of
supervised learning in which input data is continuously used to
further train the model. Incremental learning enables the trained
neural network 2908 to adapt to the new data 2912 without
forgetting the knowledge instilled within the network during
initial training.
[0347] Whether supervised or unsupervised, the training process for
particularly deep neural networks may be too computationally
intensive for a single compute node. Instead of using a single
compute node, a distributed network of computational nodes can be
used to accelerate the training process.
[0348] FIG. 30A is a block diagram illustrating distributed
learning. Distributed learning is a training model that uses
multiple distributed computing nodes such as the nodes described
above to perform supervised or unsupervised training of a neural
network. The distributed computational nodes can each include one
or more host processors and one or more of the general-purpose
processing nodes, such as a highly-parallel general-purpose
graphics processing unit. As illustrated, distributed learning can
be performed model parallelism 3002, data parallelism 3004, or a
combination of model and data parallelism.
[0349] In model parallelism 3002, different computational nodes in
a distributed system can perform training computations for
different parts of a single network. For example, each layer of a
neural network can be trained by a different processing node of the
distributed system. The benefits of model parallelism include the
ability to scale to particularly large models. Splitting the
computations associated with different layers of the neural network
enables the training of very large neural networks in which the
weights of all layers would not fit into the memory of a single
computational node. In some instances, model parallelism can be
particularly useful in performing unsupervised training of large
neural networks.
[0350] In data parallelism 3004, the different nodes of the
distributed network have a complete instance of the model and each
node receives a different portion of the data. The results from the
different nodes are then combined. While different approaches to
data parallelism are possible, data parallel training approaches
all require a technique of combining results and synchronizing the
model parameters between each node. Exemplary approaches to
combining data include parameter averaging and update based data
parallelism. Parameter averaging trains each node on a subset of
the training data and sets the global parameters (e.g., weights,
biases) to the average of the parameters from each node. Parameter
averaging uses a central parameter server that maintains the
parameter data. Update based data parallelism is similar to
parameter averaging except that instead of transferring parameters
from the nodes to the parameter server, the updates to the model
are transferred. Additionally, update based data parallelism can be
performed in a decentralized manner, where the updates are
compressed and transferred between nodes.
[0351] Combined model and data parallelism 3006 can be implemented,
for example, in a distributed system in which each computational
node includes multiple GPUs. Each node can have a complete instance
of the model with separate GPUs within each node are used to train
different portions of the model.
[0352] Distributed training has increased overhead relative to
training on a single machine. However, the parallel processors and
GPGPUs described herein can each implement various techniques to
reduce the overhead of distributed training, including techniques
to enable high bandwidth GPU-to-GPU data transfer and accelerated
remote data synchronization.
Exemplary Machine Learning Applications
[0353] Machine learning can be applied to solve a variety of
technological problems, including but not limited to computer
vision, autonomous driving and navigation, speech recognition, and
language processing. Computer vision has traditionally been one of
the most active research areas for machine learning applications.
Applications of computer vision range from reproducing human visual
abilities, such as recognizing faces, to creating new categories of
visual abilities. For example, computer vision applications can be
configured to recognize sound waves from the vibrations induced in
objects visible in a video. Parallel processor accelerated machine
learning enables computer vision applications to be trained using
significantly larger training dataset than previously feasible and
enables inferencing systems to be deployed using low power parallel
processors.
[0354] Parallel processor accelerated machine learning has
autonomous driving applications including lane and road sign
recognition, obstacle avoidance, navigation, and driving control.
Accelerated machine learning techniques can be used to train
driving models based on datasets that define the appropriate
responses to specific training input. The parallel processors
described herein can enable rapid training of the increasingly
complex neural networks used for autonomous driving solutions and
enables the deployment of low power inferencing processors in a
mobile platform suitable for integration into autonomous
vehicles.
[0355] Parallel processor accelerated deep neural networks have
enabled machine learning approaches to automatic speech recognition
(ASR). ASR includes the creation of a function that computes the
most probable linguistic sequence given an input acoustic sequence.
Accelerated machine learning using deep neural networks have
enabled the replacement of the hidden Markov models (HMMs) and
Gaussian mixture models (GMMs) previously used for ASR.
[0356] Parallel processor accelerated machine learning can also be
used to accelerate natural language processing. Automatic learning
procedures can make use of statistical inference algorithms to
produce models that are robust to erroneous or unfamiliar input.
Exemplary natural language processor applications include automatic
machine translation between human languages.
[0357] The parallel processing platforms used for machine learning
can be divided into training platforms and deployment platforms.
Training platforms are generally highly parallel and include
optimizations to accelerate multi-GPU single node training and
multi-node, multi-GPU training. Exemplary parallel processors
suited for training include the highly-parallel general-purpose
graphics processing unit and/or the multi-GPU computing systems
described herein. On the contrary, deployed machine learning
platforms generally include lower power parallel processors
suitable for use in products such as cameras, autonomous robots,
and autonomous vehicles.
[0358] FIG. 30B illustrates an exemplary inferencing system on a
chip (SOC) 3100 suitable for performing inferencing using a trained
model. The elements of FIG. 30B having the same or similar names as
the elements of any other figure herein describe the same elements
as in the other figures, can operate or function in a manner
similar to that, can comprise the same components, and can be
linked to other entities, as those described elsewhere herein, but
are not limited to such. The SOC 3100 can integrate processing
components including a media processor 3102, a vision processor
3104, a GPGPU 3106 and a multi-core processor 3108. The SOC 3100
can additionally include on-chip memory 3105 that can enable a
shared on-chip data pool that is accessible by each of the
processing components. The processing components can be optimized
for low power operation to enable deployment to a variety of
machine learning platforms, including autonomous vehicles and
autonomous robots. For example, one implementation of the SOC 3100
can be used as a portion of the main control system for an
autonomous vehicle. Where the SOC 3100 is configured for use in
autonomous vehicles the SOC is designed and configured for
compliance with the relevant functional safety standards of the
deployment jurisdiction.
[0359] During operation, the media processor 3102 and vision
processor 3104 can work in concert to accelerate computer vision
operations. The media processor 3102 can enable low latency decode
of multiple high-resolution (e.g., 4K, 8K) video streams. The
decoded video streams can be written to a buffer in the
on-chip-memory 3105. The vision processor 3104 can then parse the
decoded video and perform preliminary processing operations on the
frames of the decoded video in preparation of processing the frames
using a trained image recognition model. For example, the vision
processor 3104 can accelerate convolution operations for a CNN that
is used to perform image recognition on the high-resolution video
data, while back end model computations are performed by the GPGPU
3106.
[0360] The multi-core processor 3108 can include control logic to
assist with sequencing and synchronization of data transfers and
shared memory operations performed by the media processor 3102 and
the vision processor 3104. The multi-core processor 3108 can also
function as an application processor to execute software
applications that can make use of the inferencing compute
capability of the GPGPU 3106. For example, at least a portion of
the navigation and driving logic can be implemented in software
executing on the multi-core processor 3108. Such software can
directly issue computational workloads to the GPGPU 3106 or the
computational workloads can be issued to the multi-core processor
3108, which can offload at least a portion of those operations to
the GPGPU 3106.
[0361] The GPGPU 3106 can include processing clusters such as a low
power configuration of the processing clusters DPLAB06A-DPLAB06H
within the highly-parallel general-purpose graphics processing unit
DPLAB00. The processing clusters within the GPGPU 3106 can support
instructions that are specifically optimized to perform inferencing
computations on a trained neural network. For example, the GPGPU
3106 can support instructions to perform low precision computations
such as 8-bit and 4-bit integer vector operations.
Ray Tracing Architecture
[0362] In one implementation, the graphics processor includes
circuitry and/or program code for performing real-time ray tracing.
A dedicated set of ray tracing cores may be included in the
graphics processor to perform the various ray tracing operations
described herein, including ray traversal and/or ray intersection
operations. In addition to the ray tracing cores, multiple sets of
graphics processing cores for performing programmable shading
operations and multiple sets of tensor cores for performing matrix
operations on tensor data may also be included.
[0363] FIG. 31 illustrates an exemplary portion of one such
graphics processing unit (GPU) 3105 which includes dedicated sets
of graphics processing resources arranged into multi-core groups
3100A-N. The graphics processing unit (GPU) 3105 may be a variant
of the graphics processor 300, the GPGPU 1340 and/or any other
graphics processor described herein. Therefore, the disclosure of
any features for graphics processors also discloses a corresponding
combination with the GPU 3105, but is not limited to such.
Moreover, the elements of FIG. 31 having the same or similar names
as the elements of any other figure herein describe the same
elements as in the other figures, can operate or function in a
manner similar to that, can comprise the same components, and can
be linked to other entities, as those described elsewhere herein,
but are not limited to such. While the details of only a single
multi-core group 3100A are provided, it will be appreciated that
the other multi-core groups 3100B-N may be equipped with the same
or similar sets of graphics processing resources.
[0364] As illustrated, a multi-core group 3100A may include a set
of graphics cores 3130, a set of tensor cores 3140, and a set of
ray tracing cores 3150. A scheduler/dispatcher 3110 schedules and
dispatches the graphics threads for execution on the various cores
3130, 3140, 3150. A set of register files 3120 store operand values
used by the cores 3130, 3140, 3150 when executing the graphics
threads. These may include, for example, integer registers for
storing integer values, floating point registers for storing
floating point values, vector registers for storing packed data
elements (integer and/or floating point data elements) and tile
registers for storing tensor/matrix values. The tile registers may
be implemented as combined sets of vector registers.
[0365] One or more Level 1 (L1) caches and texture units 3160 store
graphics data such as texture data, vertex data, pixel data, ray
data, bounding volume data, etc, locally within each multi-core
group 3100A. A Level 2 (L2) cache 3180 shared by all or a subset of
the multi-core groups 3100A-N stores graphics data and/or
instructions for multiple concurrent graphics threads. As
illustrated, the L2 cache 3180 may be shared across a plurality of
multi-core groups 3100A-N. One or more memory controllers 3170
couple the GPU 3105 to a memory 3198 which may be a system memory
(e.g., DRAM) and/or a local graphics memory (e.g., GDDR6
memory).
[0366] Input/output (IO) circuitry 3195 couples the GPU 3105 to one
or more IO devices 3195 such as digital signal processors (DSPs),
network controllers, or user input devices. An on-chip interconnect
may be used to couple the I/O devices 3190 to the GPU 3105 and
memory 3198. One or more IO memory management units (IOMMUs) 3170
of the IO circuitry 3195 couple the IO devices 3190 directly to the
system memory 3198. The IOMMU 3170 may manage multiple sets of page
tables to map virtual addresses to physical addresses in system
memory 3198. Additionally, the IO devices 3190, CPU(s) 3199, and
GPU(s) 3105 may share the same virtual address space.
[0367] The IOMMU 3170 may also support virtualization. In this
case, it may manage a first set of page tables to map
guest/graphics virtual addresses to guest/graphics physical
addresses and a second set of page tables to map the guest/graphics
physical addresses to system/host physical addresses (e.g., within
system memory 3198). The base addresses of each of the first and
second sets of page tables may be stored in control registers and
swapped out on a context switch (e.g., so that the new context is
provided with access to the relevant set of page tables). While not
illustrated in FIG. 31, each of the cores 3130, 3140, 3150 and/or
multi-core groups 3100A-N may include translation lookaside buffers
(TLBs) to cache guest virtual to guest physical translations, guest
physical to host physical translations, and guest virtual to host
physical translations.
[0368] The CPUs 3199, GPUs 3105, and IO devices 3190 can be
integrated on a single semiconductor chip and/or chip package. The
illustrated memory 3198 may be integrated on the same chip or may
be coupled to the memory controllers 3170 via an off-chip
interface. In one implementation, the memory 3198 comprises GDDR6
memory which shares the same virtual address space as other
physical system-level memories, although the underlying principles
of the invention are not limited to this specific
implementation.
[0369] The tensor cores 3140 may include a plurality of execution
units specifically designed to perform matrix operations, which are
the fundamental compute operation used to perform deep learning
operations. For example, simultaneous matrix multiplication
operations may be used for neural network training and inferencing.
The tensor cores 3140 may perform matrix processing using a variety
of operand precisions including single precision floating-point
(e.g., 32 bits), half-precision floating point (e.g., 16 bits),
integer words (16 bits), bytes (8 bits), and half-bytes (4 bits). A
neural network implementation may also extract features of each
rendered scene, potentially combining details from multiple frames,
to construct a high-quality final image.
[0370] In deep learning implementations, parallel matrix
multiplication work may be scheduled for execution on the tensor
cores 3140. The training of neural networks, in particular,
requires a significant number matrix dot product operations. In
order to process an inner-product formulation of an
N.times.N.times.N matrix multiply, the tensor cores 3140 may
include at least N dot-product processing elements. Before the
matrix multiply begins, one entire matrix is loaded into tile
registers and at least one column of a second matrix is loaded each
cycle for N cycles. Each cycle, there are N dot products that are
processed.
[0371] Matrix elements may be stored at different precisions
depending on the particular implementation, including 16-bit words,
8-bit bytes (e.g., INT8) and 4-bit half-bytes (e.g., INT4).
Different precision modes may be specified for the tensor cores
3140 to ensure that the most efficient precision is used for
different workloads (e.g., such as inferencing workloads which can
tolerate quantization to bytes and half-bytes).
[0372] The ray tracing cores 3150 may be used to accelerate ray
tracing operations for both real-time ray tracing and non-real-time
ray tracing implementations. In particular, the ray tracing cores
3150 may include ray traversal/intersection circuitry for
performing ray traversal using bounding volume hierarchies (BVHs)
and identifying intersections between rays and primitives enclosed
within the BVH volumes. The ray tracing cores 3150 may also include
circuitry for performing depth testing and culling (e.g., using a Z
buffer or similar arrangement). In one implementation, the ray
tracing cores 3150 perform traversal and intersection operations in
concert with the image denoising techniques described herein, at
least a portion of which may be executed on the tensor cores 3140.
For example, the tensor cores 3140 may implement a deep learning
neural network to perform denoising of frames generated by the ray
tracing cores 3150. However, the CPU(s) 3199, graphics cores 3130,
and/or ray tracing cores 3150 may also implement all or a portion
of the denoising and/or deep learning algorithms.
[0373] In addition, as described above, a distributed approach to
denoising may be employed in which the GPU 3105 is in a computing
device coupled to other computing devices over a network or high
speed interconnect. The interconnected computing devices may
additionally share neural network learning/training data to improve
the speed with which the overall system learns to perform denoising
for different types of image frames and/or different graphics
applications.
[0374] The ray tracing cores 3150 may process all BVH traversal and
ray-primitive intersections, saving the graphics cores 3130 from
being overloaded with thousands of instructions per ray. Each ray
tracing core 3150 may include a first set of specialized circuitry
for performing bounding box tests (e.g., for traversal operations)
and a second set of specialized circuitry for performing the
ray-triangle intersection tests (e.g., intersecting rays which have
been traversed). Thus, the multi-core group 3100A can simply launch
a ray probe, and the ray tracing cores 3150 independently perform
ray traversal and intersection and return hit data (e.g., a hit, no
hit, multiple hits, etc) to the thread context. The other cores
3130, 3140 may be freed to perform other graphics or compute work
while the ray tracing cores 3150 perform the traversal and
intersection operations.
[0375] Each ray tracing core 3150 may include a traversal unit to
perform BVH testing operations and an intersection unit which
performs ray-primitive intersection tests. The intersection unit
may then generate a "hit", "no hit", or "multiple hit" response,
which it provides to the appropriate thread. During the traversal
and intersection operations, the execution resources of the other
cores (e.g., graphics cores 3130 and tensor cores 3140) may be
freed to perform other forms of graphics work.
[0376] A hybrid rasterization/ray tracing approach may also be used
in which work is distributed between the graphics cores 3130 and
ray tracing cores 3150.
[0377] The ray tracing cores 3150 (and/or other cores 3130, 3140)
may include hardware support for a ray tracing instruction set such
as Microsoft's DirectX Ray Tracing (DXR) which includes a
DispatchRays command, as well as ray-generation, closest-hit,
any-hit, and miss shaders, which enable the assignment of unique
sets of shaders and textures for each object. Another ray tracing
platform which may be supported by the ray tracing cores 3150,
graphics cores 3130 and tensor cores 3140 is Vulkan 1.1.85. Note,
however, that the underlying principles of the invention are not
limited to any particular ray tracing ISA.
[0378] In general, the various cores 3150, 3140, 3130 may support a
ray tracing instruction set that includes instructions/functions
for ray generation, closest hit, any hit, ray-primitive
intersection, per-primitive and hierarchical bounding box
construction, miss, visit, and exceptions. More specifically, ray
tracing instructions can be included to perform the following
functions:
[0379] Ray Generation--Ray generation instructions may be executed
for each pixel, sample, or other user-defined work assignment.
[0380] Closest Hit--A closest hit instruction may be executed to
locate the closest intersection point of a ray with primitives
within a scene.
[0381] Any Hit--An any hit instruction identifies multiple
intersections between a ray and primitives within a scene,
potentially to identify a new closest intersection point.
[0382] Intersection--An intersection instruction performs a
ray-primitive intersection test and outputs a result.
[0383] Per-primitive Bounding box Construction--This instruction
builds a bounding box around a given primitive or group of
primitives (e.g., when building a new BVH or other acceleration
data structure).
[0384] Miss--Indicates that a ray misses all geometry within a
scene, or specified region of a scene.
[0385] Visit--Indicates the children volumes a ray will
traverse.
[0386] Exceptions--Includes various types of exception handlers
(e.g., invoked for various error conditions).
Hierarchical Beam Tracing
[0387] Bounding volume hierarchies are commonly used to improve the
efficiency with which operations are performed on graphics
primitives and other graphics objects. A BVH is a hierarchical tree
structure which is built based on a set of geometric objects. At
the top of the tree structure is the root node which encloses all
of the geometric objects in a given scene. The individual geometric
objects are wrapped in bounding volumes that form the leaf nodes of
the tree. These nodes are then grouped as small sets and enclosed
within larger bounding volumes. These, in turn, are also grouped
and enclosed within other larger bounding volumes in a recursive
fashion, eventually resulting in a tree structure with a single
bounding volume, represented by the root node, at the top of the
tree. Bounding volume hierarchies are used to efficiently support a
variety of operations on sets of geometric objects, such as
collision detection, primitive culling, and ray
traversal/intersection operations used in ray tracing.
[0388] In ray tracing architectures, rays are traversed through a
BVH to determine ray-primitive intersections. For example, if a ray
does not pass through the root node of the BVH, then the ray does
not intersect any of the primitives enclosed by the BVH and no
further processing is required for the ray with respect to this set
of primitives. If a ray passes through a first child node of the
BVH but not the second child node, then the ray need not be tested
against any primitives enclosed by the second child node. In this
manner, a BVH provides an efficient mechanism to test for
ray-primitive intersections.
[0389] Groups of contiguous rays, referred to as "beams" may be
tested against the BVH, rather than individual rays. FIG. 32
illustrates an exemplary beam 3201 outlined by four different rays.
Any rays which intersect the patch 3200 defined by the four rays
are considered to be within the same beam. While the beam 3201 in
FIG. 32 is defined by a rectangular arrangement of rays, beams may
be defined in various other ways while still complying with the
underlying principles of the invention (e.g., circles, ellipses,
etc).
[0390] FIG. 33 illustrates how a ray tracing engine 3310 of a GPU
3320 implements the beam tracing techniques described herein. In
particular, ray generation circuitry 3304 generates a plurality of
rays for which traversal and intersection operations are to be
performed. However, rather than performing traversal and
intersection operations on individual rays, traversal and
intersection operations are performed using a hierarchy of beams
3307 generated by beam hierarchy construction circuitry 3305. The
beam hierarchy is analogous to the bounding volume hierarchy (BVH).
For example, FIG. 34 provides an example of a primary beam 3400
which may be subdivided into a plurality of different components.
In particular, primary beam 3400 may be divided into quadrants
3401-3404 and each quadrant may itself be divided into
sub-quadrants such as sub-quadrants A-D within quadrant 3404. The
primary beam may be subdivided in a variety of ways. For example,
the primary beam may be divided in half (rather than quadrants) and
each half may be divided in half, and so on. Regardless of how the
subdivisions are made, a hierarchical structure is generated in a
similar manner as a BVH, e.g., with a root node representing the
primary beam 3400, a first level of child nodes, each represented
by a quadrant 3401-3404, second level child nodes for each
sub-quadrant A-D, and so on.
[0391] Once the beam hierarchy 3307 is constructed,
traversal/intersection circuitry 3306 may perform
traversal/intersection operations using the beam hierarchy 3307 and
the BVH 3308. In particular, it may test the beam against the BVH
and cull portions of the beam which do not intersect any portions
of the BVH. Using the data shown in FIG. 34, for example, if the
sub-beams associated with sub-regions 3402 and 3403 do not
intersect with the BVH or a particular branch of the BVH, then they
may be culled with respect to the BVH or the branch. The remaining
portions 3401, 3404 may be tested against the BVH by performing a
depth-first search or other search algorithm.
[0392] A method for ray-tracing is illustrated in FIG. 35. The
method may be implemented within the context of the graphics
processing architectures described above, but is not limited to any
particular architecture.
[0393] At 3500 a primary beam is constructed comprising a plurality
of rays and at 3501, the beam is subdivided and hierarchical data
structures generated to create a beam hierarchy. The operations
3500-3501 may be performed as a single, integrated operation which
constructs a beam hierarchy from a plurality of rays. At 3502, the
beam hierarchy is used with a BVH to cull rays (from the beam
hierarchy) and/or nodes/primitives from the BVH. At 3503,
ray-primitive intersections are determined for the remaining rays
and primitives.
Lossy and Lossless Packet Compression in a Distributed Ray Tracing
System
[0394] Ray tracing operations may be distributed across a plurality
of compute nodes coupled together over a network. FIG. 36, for
example, illustrates a ray tracing cluster 3600 comprising a
plurality of ray tracing nodes 3610-3613 perform ray tracing
operations in parallel, potentially combining the results on one of
the nodes. In the illustrated architecture, the ray tracing nodes
3610-3613 are communicatively coupled to a client-side ray tracing
application 3630 via a gateway.
[0395] One of the difficulties with a distributed architecture is
the large amount of packetized data that must be transmitted
between each of the ray tracing nodes 3610-3613. Both lossless
compression techniques and lossy compression techniques may be used
to reduce the data transmitted between the ray tracing nodes
3610-3613.
[0396] To implement lossless compression, rather than sending
packets filled with the results of certain types of operations,
data or commands are sent which allow the receiving node to
reconstruct the results. For example, stochastically sampled area
lights and ambient occlusion (AO) operations do not necessarily
need directions. Consequently, a transmitting node can simply send
a random seed which is then used by the receiving node to perform
random sampling. For example, if a scene is distributed across
nodes 3610-3612, to sample light 1 at points p1-p3, only the light
ID and origins need to be sent to nodes 3610-3612. Each of the
nodes may then stochastically sample the light independently. The
random seed may be generated by the receiving node. Similarly, for
primary ray hit points, ambient occlusion (AO) and soft shadow
sampling can be computed on nodes 3610-3612 without waiting for the
original points for successive frames. Additionally, if it is known
that a set of rays will go to the same point light source,
instructions may be sent identifying the light source to the
receiving node which will apply it to the set of rays. As another
example, if there are N ambient occlusion rays transmitted a single
point, a command may be sent to generate N samples from this
point.
[0397] Various additional techniques may be applied for lossy
compression. For example, a quantization factor may be employed to
quantize all coordinate values associated with the BVH, primitives,
and rays. In addition, 32-bit floating point values used for data
such as BVH nodes and primitives may be converted into 8-bit
integer values. In an exemplary implementation, the bounds of ray
packets are stored in in full precision but individual ray points
P1-P3 are transmitted as indexed offsets to the bounds. Similarly,
a plurality of local coordinate systems may be generated which use
8-bit integer values as local coordinates. The location of the
origin of each of these local coordinate systems may be encoded
using the full precision (e.g., 32-bit floating point) values,
effectively connecting the global and local coordinate systems.
[0398] The following is an example of lossless compression. An
example of a Ray data format used internally in a ray tracing
program is as follows:
TABLE-US-00001 struct Ray { uint32 pixId; uint32 materialID; uint32
instanceID; uint64 primitiveID; uint32 geometryID; uint32 lightID;
float origin[3]; float direction[3]; float t0; float t; float time;
float normal[3]; //used for geometry intersections float u; float
v; float wavelength; float phase; //Interferometry float
refractedOffset; //Schlieren-esque float amplitude; float weight;
};
[0399] Instead of sending the raw data for each and every node
generated, this data can be compressed by grouping values and by
creating implicit rays using applicable metadata where
possible.
[0400] Bundling and Grouping Ray Data
Flags may be used for common data or masks with modifiers.
TABLE-US-00002 struct RayPacket { uint32 size; uint32 flags;
list<Ray> rays; }
For example: [0401] RayPacket.rays=ray_1 to ray_256
Origins are all Shared
[0402] All ray data is packed, except only a single origin is
stored across all rays. RayPacket.flags is set for
RAYPACKET_COMMON_ORIGIN. When RayPacket is unpacked when received,
origins are filled in from the single origin value.
Origins are Shared Only Among Some Rays
[0403] All ray data is packed, except for rays that share origins.
For each group of unique shared origins, an operator is packed on
that identifies the operation (shared origins), stores the origin,
and masks which rays share the information. Such an operation can
be done on any shared values among nodes such as material IDs,
primitive IDs, origin, direction, normals, etc.
TABLE-US-00003 struct RayOperation { uint8 operationID; void*
value; uint64 mask; }
Sending Implicit Rays
[0404] Often times, ray data can be derived on the receiving end
with minimal meta information used to generate it. A very common
example is generating multiple secondary rays to stochastically
sample an area. Instead of the sender generating a secondary ray,
sending it, and the receiver operating on it, the sender can send a
command that a ray needs to be generated with any dependent
information, and the ray is generated on the receiving end. In the
case where the ray needs to be first generated by the sender to
determine which receiver to send it to, the ray is generated and
the random seed can be sent to regenerate the exact same ray.
[0405] For example, to sample a hit point with 64 shadow rays
sampling an area light source, all 64 rays intersect with regions
from the same compute N4. A RayPacket with common origin and normal
is created. More data could be sent if one wished the receiver to
shade the resulting pixel contribution, but for this example let us
assume we wish to only return whether a ray hits another nodes
data. A RayOperation is created for a generate shadow ray
operation, and is assigned the value of the lightID to be sampled
and the random number seed. When N4 receives the ray packet, it
generates the fully filled Ray data by filling in the shared origin
data to all rays and setting the direction based on the lightID
stochastically sampled with the random number seed to generate the
same rays that the original sender generated. When the results are
returned, only binary results for every ray need be returned, which
can be handed by a mask over the rays.
[0406] Sending the original 64 rays in this example would have used
104 Bytes*64 rays=6656 Bytes. If the returning rays were sent in
their raw form as well, than this is also doubled to 13312 Bytes.
Using lossless compression with only sending the common ray origin,
normal, and ray generation operation with seed and ID, only 29
Bytes are sent with 8 Bytes returned for the was intersected mask.
This results in a data compression rate that needs to be sent over
the network of .about.360:1. This does not include overhead to
process the message itself, which would need to be identified in
some way, but that is left up to the implementation. Other
operations may be done for recomputing ray origin and directions
from the pixeID for primary rays, recalculating pixelIDs based on
the ranges in the raypacket, and many other possible
implementations for recomputation of values. Similar operations can
be used for any single or group of rays sent, including shadows,
reflections, refraction, ambient occlusion, intersections, volume
intersections, shading, bounced reflections in path tracing,
etc.
[0407] FIG. 37 illustrates additional details for two ray tracing
nodes 3710-3711 which perform compression and decompression of ray
tracing packets. In particular, when a first ray tracing engine
3730 is ready to transmit data to a second ray tracing engine 3731,
ray compression circuitry 3720 performs lossy and/or lossless
compression of the ray tracing data as described herein (e.g.,
converting 32-bit values to 8-bit values, substituting raw data for
instructions to reconstruct the data, etc). The compressed ray
packets 3701 are transmitted from network interface 3725 to network
interface 3726 over a local network (e.g., a 10 Gb/s, 100 Gb/s
Ethernet network). Ray decompression circuitry then decompresses
the ray packets when appropriate. For example, it may execute
commands to reconstruct the ray tracing data (e.g., using a random
seed to perform random sampling for lighting operations). Ray
tracing engine 3731 then uses the received data to perform ray
tracing operations.
[0408] In the reverse direction, ray compression circuitry 3741
compresses ray data, network interface 3726 transmits the
compressed ray data over the network (e.g., using the techniques
described herein), ray decompression circuitry 3740 decompresses
the ray data when necessary and ray tracing engine 3730 uses the
data in ray tracing operations. Although illustrated as a separate
unit in FIG. 37, ray decompression circuitry 3740-3741 may be
integrated within ray tracing engines 3730-3731, respectively. For
example, to the extent the compressed ray data comprises commands
to reconstruct the ray data, these commands may be executed by each
respective ray tracing engine 3730-3731.
[0409] As illustrated in FIG. 38, ray compression circuitry 3720
may include lossy compression circuitry 3801 for performing the
lossy compression techniques described herein (e.g., converting
32-bit floating point coordinates to 8-bit integer coordinates) and
lossless compression circuitry 3803 for performing the lossless
compression techniques (e.g., transmitting commands and data to
allow ray recompression circuitry 3821 to reconstruct the data).
Ray decompression circuitry 3721 includes lossy decompression
circuitry 3802 and lossless decompression circuitry 3804 for
performing lossless decompression.
[0410] Another exemplary method is illustrated in FIG. 39. The
method may be implemented on the ray tracing architectures or other
architectures described herein but is not limited to any particular
architecture.
[0411] At 3900, ray data is received which will be transmitted from
a first ray tracing node to a second ray tracing node. At 3901,
lossy compression circuitry performs lossy compression on first ray
tracing data and, at 3902, lossless compression circuitry performs
lossless compression on second ray tracing data. At 3903, the
compressed ray racing data is transmitted to a second ray tracing
node. At 3904, lossy/lossless decompression circuitry performs
lossy/lossless decompression of the ray tracing data and, at 3905,
the second ray tracing node performs ray tracing operations sing
the decompressed data.
Graphics Processor with Hardware Accelerated Hybrid Ray Tracing
[0412] A hybrid rendering pipeline which performs rasterization on
graphics cores 3130 and ray tracing operations on the ray tracing
cores 3150, graphics cores 3130, and/or CPU 3199 cores, is
presented next. For example, rasterization and depth testing may be
performed on the graphics cores 3130 in place of the primary ray
casting stage. The ray tracing cores 3150 may then generate
secondary rays for ray reflections, refractions, and shadows. In
addition, certain regions of a scene in which the ray tracing cores
3150 will perform ray tracing operations (e.g., based on material
property thresholds such as high reflectivity levels) will be
selected while other regions of the scene will be rendered with
rasterization on the graphics cores 3130. This hybrid
implementation may be used for real-time ray tracing
applications--where latency is a critical issue.
[0413] The ray traversal architecture described below may, for
example, perform programmable shading and control of ray traversal
using existing single instruction multiple data (SIMD) and/or
single instruction multiple thread (SIMT) graphics processors while
accelerating critical functions, such as BVH traversal and/or
intersections, using dedicated hardware. SIMD occupancy for
incoherent paths may be improved by regrouping spawned shaders at
specific points during traversal and before shading. This is
achieved using dedicated hardware that sorts shaders dynamically,
on-chip. Recursion is managed by splitting a function into
continuations that execute upon returning and regrouping
continuations before execution for improved SIMD occupancy.
[0414] Programmable control of ray traversal/intersection is
achieved by decomposing traversal functionality into an inner
traversal that can be implemented as fixed function hardware and an
outer traversal that executes on GPU processors and enables
programmable control through user defined traversal shaders. The
cost of transferring the traversal context between hardware and
software is reduced by conservatively truncating the inner
traversal state during the transition between inner and outer
traversal.
[0415] Programmable control of ray tracing can be expressed through
the different shader types listed in Table A below. There can be
multiple shaders for each type. For example each material can have
a different hit shader.
TABLE-US-00004 TABLE A Shader Type Functionality Primary Launching
primary rays Hit Bidirectional reflectance distribution function
(BRDF) sampling, launching secondary rays Any Hit Computing
transmittance for alpha textured geometry Miss Computing radiance
from a light source Intersection Intersecting custom shapes
Traversal Instance selection and transformation Callable A
general-purpose function
[0416] Recursive ray tracing may be initiated by an API function
that commands the graphics processor to launch a set of primary
shaders or intersection circuitry which can spawn ray-scene
intersections for primary rays. This in turn spawns other shaders
such as traversal, hit shaders, or miss shaders. A shader that
spawns a child shader can also receive a return value from that
child shader. Callable shaders are general-purpose functions that
can be directly spawned by another shader and can also return
values to the calling shader.
[0417] FIG. 40 illustrates a graphics processing architecture which
includes shader execution circuitry 4000 and fixed function
circuitry 4010. The general purpose execution hardware subsystem
includes a plurality of single instruction multiple data (SIMD)
and/or single instructions multiple threads (SIMT) cores/execution
units (EUs) 4001 (i.e., each core may comprise a plurality of
execution units), one or more samplers 4002, and a Level 1 (L1)
cache 4003 or other form of local memory. The fixed function
hardware subsystem 4010 includes message unit 4004, a scheduler
4007, ray-BVH traversal/intersection circuitry 4005, sorting
circuitry 4008, and a local L1 cache 4006.
[0418] In operation, primary dispatcher 4009 dispatches a set of
primary rays to the scheduler 4007, which schedules work to shaders
executed on the SIMD/SIMT cores/EUs 4001. The SIMD cores/EUs 4001
may be ray tracing cores 3150 and/or graphics cores 3130 described
above. Execution of the primary shaders spawns additional work to
be performed (e.g., to be executed by one or more child shaders
and/or fixed function hardware). The message unit 4004 distributes
work spawned by the SIMD cores/EUs 4001 to the scheduler 4007,
accessing the free stack pool as needed, the sorting circuitry
4008, or the ray-BVH intersection circuitry 4005. If the additional
work is sent to the scheduler 4007, it is scheduled for processing
on the SIMD/SIMT cores/EUs 4001. Prior to scheduling, the sorting
circuitry 4008 may sort the rays into groups or bins as described
herein (e.g., grouping rays with similar characteristics). The
ray-BVH intersection circuitry 4005 performs intersection testing
of rays using BVH volumes. For example, the ray-BVH intersection
circuitry 4005 may compare ray coordinates with each level of the
BVH to identify volumes which are intersected by the ray.
[0419] Shaders can be referenced using a shader record, a
user-allocated structure that includes a pointer to the entry
function, vendor-specific metadata, and global arguments to the
shader executed by the SIMD cores/EUs 4001. Each executing instance
of a shader is associated with a call stack which may be used to
store arguments passed between a parent shader and child shader.
Call stacks may also store references to the continuation functions
that are executed when a call returns.
[0420] FIG. 41 illustrates an example set of assigned stacks 4101
which includes a primary shader stack, a hit shader stack, a
traversal shader stack, a continuation function stack, and a
ray-BVH intersection stack (which, as described, may be executed by
fixed function hardware 4010). New shader invocations may implement
new stacks from a free stack pool 4102. The call stacks, e.g.
stacks comprised by the set of assigned stacks, may be cached in a
local L1 cache 4003, 4006 to reduce the latency of accesses.
[0421] There may be a finite number of call stacks, each with a
fixed maximum size "Sstack" allocated in a contiguous region of
memory. Therefore the base address of a stack can be directly
computed from a stack index (SID) as base address=SID*Sstack. Stack
IDs may be allocated and deallocated by the scheduler 4007 when
scheduling work to the SIMD cores/EUs 4001.
[0422] The primary dispatcher 4009 may comprise a graphics
processor command processor which dispatches primary shaders in
response to a dispatch command from the host (e.g., a CPU). The
scheduler 4007 may receive these dispatch requests and launches a
primary shader on a SIMD processor thread if it can allocate a
stack ID for each SIMD lane. Stack IDs may be allocated from the
free stack pool 4102 that is initialized at the beginning of the
dispatch command.
[0423] An executing shader can spawn a child shader by sending a
spawn message to the messaging unit 4004. This command includes the
stack IDs associated with the shader and also includes a pointer to
the child shader record for each active SIMD lane. A parent shader
can only issue this message once for an active lane. After sending
spawn messages for all relevant lanes, the parent shader may
terminate.
[0424] A shader executed on the SIMD cores/EUs 4001 can also spawn
fixed-function tasks such as ray-BVH intersections using a spawn
message with a shader record pointer reserved for the
fixed-function hardware. As mentioned, the messaging unit 4004
sends spawned ray-BVH intersection work to the fixed-function
ray-BVH intersection circuitry 4005 and callable shaders directly
to the sorting circuitry 4008. The sorting circuitry may group the
shaders by shader record pointer to derive a SIMD batch with
similar characteristics. Accordingly, stack IDs from different
parent shaders can be grouped by the sorting circuitry 4008 in the
same batch. The sorting circuitry 4008 sends grouped batches to the
scheduler 4007 which accesses the shader record from graphics
memory 2511 or the last level cache (LLC) 4020 and launches the
shader on a processor thread.
[0425] Continuations may be treated as callable shaders and may
also be referenced through shader records. When a child shader is
spawned and returns values to the parent shader, a pointer to the
continuation shader record may be pushed on the call stack 4101.
When a child shader returns, the continuation shader record may
then be popped from the call stack 4101 and a continuation shader
may be spawned. Optionally, spawned continuations may go through
the sorting unit similar to callable shaders and get launched on a
processor thread.
[0426] As illustrated in FIG. 42, the sorting circuitry 4008 groups
spawned tasks by shader record pointers 4201A, 4201B, 4201n to
create SIMD batches for shading. The stack IDs or context IDs in a
sorted batch can be grouped from different dispatches and different
input SIMD lanes. A grouping circuitry 4210 may perform the sorting
using a content addressable memory (CAM) structure 4201 comprising
a plurality of entries with each entry identified with a tag 4201.
As mentioned, the tag 4201 may be a corresponding shader record
pointer 4201A, 4201B, 4201n. The CAM structure 4201 may store a
limited number of tags (e.g. 32, 64, 128, etc) each associated with
an incomplete SIMD batch corresponding to a shader record
pointer.
[0427] For an incoming spawn command, each SIMD lane has a
corresponding stack ID (shown as 16 context IDs 0-15 in each CAM
entry) and a shader record pointer 4201A-B, . . . n (acting as a
tag value). The grouping circuitry 4210 may compare the shader
record pointer for each lane against the tags 4201 in the CAM
structure 4201 to find a matching batch. If a matching batch is
found, the stack ID/context ID may be added to the batch. Otherwise
a new entry with a new shader record pointer tag may be created,
possibly evicting an older entry with an incomplete batch.
[0428] An executing shader can deallocate the call stack when it is
empty by sending a deallocate message to the message unit. The
deallocate message is relayed to the scheduler which returns stack
IDs/context IDs for active SIMD lanes to the free pool.
[0429] A hybrid approach for ray traversal operations, using a
combination of fixed-function ray traversal and software ray
traversal, is presented. Consequently, it provides the flexibility
of software traversal while maintaining the efficiency of
fixed-function traversal. FIG. 43 shows an acceleration structure
which may be used for hybrid traversal, which is a two-level tree
with a single top level BVH 4300 and several bottom level BVHs 4301
and 4302. Graphical elements are shown to the right to indicate
inner traversal paths 4303, outer traversal paths 4304, traversal
nodes 4305, leaf nodes with triangles 4306, and leaf nodes with
custom primitives 4307.
[0430] The leaf nodes with triangles 4306 in the top level BVH 4300
can reference triangles, intersection shader records for custom
primitives or traversal shader records. The leaf nodes with
triangles 4306 of the bottom level BVHs 4301-4302 can only
reference triangles and intersection shader records for custom
primitives. The type of reference is encoded within the leaf node
4306. Inner traversal 4303 refers to traversal within each BVH
4300-4302. Inner traversal operations comprise computation of
ray-BVH intersections and traversal across the BVH structures
4300-4302 is known as outer traversal. Inner traversal operations
can be implemented efficiently in fixed function hardware while
outer traversal operations can be performed with acceptable
performance with programmable shaders. Consequently, inner
traversal operations may be performed using fixed-function
circuitry 4010 and outer traversal operations may be performed
using the shader execution circuitry 4000 including SIMD/SIMT
cores/EUs 4001 for executing programmable shaders.
[0431] Note that the SIMD/SIMT cores/EUs 4001 are sometimes simply
referred to herein as "cores," "SIMD cores," "EUs," or "SIMD
processors" for simplicity. Similarly, the ray-BVH
traversal/intersection circuitry 4005 is sometimes simply referred
to as a "traversal unit," "traversal/intersection unit" or
"traversal/intersection circuitry." When an alternate term is used,
the particular name used to designate the respective
circuitry/logic does not alter the underlying functions which the
circuitry/logic performs, as described herein.
[0432] Moreover, while illustrated as a single component in FIG. 40
for purposes of explanation, the traversal/intersection unit 4005
may comprise a distinct traversal unit and a separate intersection
unit, each of which may be implemented in circuitry and/or logic as
described herein.
[0433] When a ray intersects a traversal node during an inner
traversal, a traversal shader may be spawned. The sorting circuitry
4008 may group these shaders by shader record pointers 4201A-B, n
to create a SIMD batch which is launched by the scheduler 4007 for
SIMD execution on the graphics SIMD cores/EUs 4001. Traversal
shaders can modify traversal in several ways, enabling a wide range
of applications. For example, the traversal shader can select a BVH
at a coarser level of detail (LOD) or transform the ray to enable
rigid body transformations. The traversal shader may then spawn
inner traversal for the selected BVH.
[0434] Inner traversal computes ray-BVH intersections by traversing
the BVH and computing ray-box and ray-triangle intersections. Inner
traversal is spawned in the same manner as shaders by sending a
message to the messaging circuitry 4004 which relays the
corresponding spawn message to the ray-BVH intersection circuitry
4005 which computes ray-BVH intersections.
[0435] The stack for inner traversal may be stored locally in the
fixed-function circuitry 4010 (e.g., within the L1 cache 4006).
When a ray intersects a leaf node corresponding to a traversal
shader or an intersection shader, inner traversal may be terminated
and the inner stack truncated. The truncated stack along with a
pointer to the ray and BVH may be written to memory at a location
specified by the calling shader and then the corresponding
traversal shader or intersection shader may be spawned. If the ray
intersects any triangles during inner traversal, the corresponding
hit information may be provided as input arguments to these shaders
as shown in the below code. These spawned shaders may be grouped by
the sorting circuitry 4008 to create SIMD batches for
execution.
TABLE-US-00005 struct HitInfo { float barycentrics[2]; float tmax;
bool innerTravComplete; uint primID; uint geomID; ShaderRecord*
leafShaderRecord; }
[0436] Truncating the inner traversal stack reduces the cost of
spilling it to memory. The approach described in Restart Trail for
Stackless BVH Traversal, High Performance Graphics (2010), pp.
107-111, to truncate the stack to a small number of entries at the
top of the stack, a 42-bit restart trail and a 6-bit depth value
may be applied. The restart trail indicates branches that have
already been taken inside the BVH and the depth value indicates the
depth of traversal corresponding to the last stack entry. This is
sufficient information to resume inner traversal at a later
time.
[0437] Inner traversal is complete when the inner stack is empty
and there no more BVH nodes to test. In this case an outer stack
handler is spawned that pops the top of the outer stack and resumes
traversal if the outer stack is not empty.
[0438] Outer traversal may execute the main traversal state machine
and may be implemented in program code executed by the shader
execution circuitry 4000. It may spawn an inner traversal query
under the following conditions: (1) when a new ray is spawned by a
hit shader or a primary shader; (2) when a traversal shader selects
a BVH for traversal; and (3) when an outer stack handler resumes
inner traversal for a BVH.
[0439] As illustrated in FIG. 44, before inner traversal is
spawned, space is allocated on the call stack 4405 for the
fixed-function circuitry 4010 to store the truncated inner stack
4410. Offsets 4403-4404 to the top of the call stack and the inner
stack are maintained in the traversal state 4400 which is also
stored in memory 2511. The traversal state 4400 also includes the
ray in world space 4401 and object space 4402 as well as hit
information for the closest intersecting primitive.
[0440] The traversal shader, intersection shader and outer stack
handler are all spawned by the ray-BVH intersection circuitry 4005.
The traversal shader allocates on the call stack 4405 before
initiating a new inner traversal for the second level BVH. The
outer stack handler is a shader that is responsible for updating
the hit information and resuming any pending inner traversal tasks.
The outer stack handler is also responsible for spawning hit or
miss shaders when traversal is complete. Traversal is complete when
there are no pending inner traversal queries to spawn. When
traversal is complete and an intersection is found, a hit shader is
spawned; otherwise a miss shader is spawned.
[0441] While the hybrid traversal scheme described above uses a
two-level BVH hierarchy, an arbitrary number of BVH levels with a
corresponding change in the outer traversal implementation may also
be implemented.
[0442] In addition, while fixed function circuitry 4010 is
described above for performing ray-BVH intersections, other system
components may also be implemented in fixed function circuitry. For
example, the outer stack handler described above may be an internal
(not user visible) shader that could potentially be implemented in
the fixed function BVH traversal/intersection circuitry 4005. This
implementation may be used to reduce the number of dispatched
shader stages and round trips between the fixed function
intersection hardware 4005 and the processor.
[0443] The examples described herein enable programmable shading
and ray traversal control using user-defined functions that can
execute with greater SIMD efficiency on existing and future GPU
processors. Programmable control of ray traversal enables several
important features such as procedural instancing, stochastic
level-of-detail selection, custom primitive intersection and lazy
BVH updates.
[0444] A programmable, multiple instruction multiple data (MIMD)
ray tracing architecture which supports speculative execution of
hit and intersection shaders is also provided. In particular, the
architecture focuses on reducing the scheduling and communication
overhead between the programmable SIMD/SIMT cores/execution units
4001 described above with respect to FIG. 40 and fixed-function
MIMD traversal/intersection units 4005 in a hybrid ray tracing
architecture. Multiple speculative execution schemes of hit and
intersection shaders are described below that can be dispatched in
a single batch from the traversal hardware, avoiding several
traversal and shading round trips. A dedicated circuitry to
implement these techniques may be used.
[0445] The embodiments of the invention are particularly beneficial
in use-cases where the execution of multiple hit or intersection
shaders is desired from a ray traversal query that would impose
significant overhead when implemented without dedicated hardware
support. These include, but are not limited to nearest k-hit query
(launch a hit shader for the k closest intersections) and multiple
programmable intersection shaders.
[0446] The techniques described here may be implemented as
extensions to the architecture illustrated in FIG. 40 (and
described with respect to FIGS. 40-44). In particular, the present
embodiments of the invention build on this architecture with
enhancements to improve the performance of the above-mentioned
use-cases.
[0447] A performance limitation of hybrid ray tracing traversal
architectures is the overhead of launching traversal queries from
the execution units and the overhead of invoking programmable
shaders from the ray tracing hardware. When multiple hit or
intersection shaders are invoked during the traversal of the same
ray, this overhead generates "execution roundtrips" between the
programmable cores 4001 and traversal/intersection unit 4005. This
also places additional pressure to the sorting unit 4008 which
needs to extract SIMD/SIMT coherence from the individual shader
invocations.
[0448] Several aspects of ray tracing require programmable control
which can be expressed through the different shader types listed in
TABLE A above (i.e., Primary, Hit, Any Hit, Miss, Intersection,
Traversal, and Callable). There can be multiple shaders for each
type. For example each material can have a different hit shader.
Some of these shader types are defined in the current
Microsoft.RTM. Ray Tracing API.
[0449] As a brief review, recursive ray tracing is initiated by an
API function that commands the GPU to launch a set of primary
shaders which can spawn ray-scene intersections (implemented in
hardware and/or software) for primary rays. This in turn can spawn
other shaders such as traversal, hit or miss shaders. A shader that
spawns a child shader can also receive a return value from that
shader. Callable shaders are general-purpose functions that can be
directly spawned by another shader and can also return values to
the calling shader.
[0450] Ray traversal computes ray-scene intersections by traversing
and intersecting nodes in a bounding volume hierarchy (BVH). Recent
research has shown that the efficiency of computing ray-scene
intersections can be improved by over an order of magnitude using
techniques that are better suited to fixed-function hardware such
as reduced-precision arithmetic, BVH compression, per-ray state
machines, dedicated intersection pipelines and custom caches.
[0451] The architecture shown in FIG. 40 comprises such a system
where an array of SIMD/SIMT cores/execution units 4001 interact
with a fixed function ray tracing/intersection unit 4005 to perform
programmable ray tracing. Programmable shaders are mapped to
SIMD/SIMT threads on the execution units/cores 4001, where
SIMD/SIMT utilization, execution, and data coherence are critical
for optimal performance. Ray queries often break up coherence for
various reasons such as: [0452] Traversal divergence: The duration
of the BVH traversal varies highly [0453] among rays favoring
asynchronous ray processing. [0454] Execution divergence: Rays
spawned from different lanes of the same SIMD/SIMT thread may
result in different shader invocations. [0455] Data access
divergence: Rays hitting different surfaces sample different BVH
nodes and primitives and shaders access different textures, for
example. A variety of other scenarios may cause data access
divergence.
[0456] The SIMD/SIMT cores/execution units 4001 may be variants of
cores/execution units described herein including graphics core(s)
415A-415B, shader cores 1355A-N, graphics cores 3130, graphics
execution unit 608, execution units 852A-B, or any other
cores/execution units described herein. The SIMD/SIMT
cores/execution units 4001 may be used in place of the graphics
core(s) 415A-415B, shader cores 1355A-N, graphics cores 3130,
graphics execution unit 608, execution units 852A-B, or any other
cores/execution units described herein. Therefore, the disclosure
of any features in combination with the graphics core(s) 415A-415B,
shader cores 1355A-N, graphics cores 3130, graphics execution unit
608, execution units 852A-B, or any other cores/execution units
described herein also discloses a corresponding combination with
the SIMD/SIMT cores/execution units 4001 of FIG. 40, but is not
limited to such.
[0457] The fixed-function ray tracing/intersection unit 4005 may
overcome the first two challenges by processing each ray
individually and out-of-order. That, however, breaks up SIMD/SIMT
groups. The sorting unit 4008 is hence responsible for forming new,
coherent SIMD/SIMT groups of shader invocations to be dispatched to
the execution units again.
[0458] It is easy to see the benefits of such an architecture
compared to a pure software-based ray tracing implementation
directly on the SIMD/SIMT processors. However, there is an overhead
associated with the messaging between the SIMD/SIMT cores/execution
units 4001 (sometimes simply referred to herein as SIMD/SIMT
processors or cores/EUs) and the MIMD traversal/intersection unit
4005. Furthermore, the sorting unit 4008 may not extract perfect
SIMD/SIMT utilization from incoherent shader calls.
[0459] Use-cases can be identified where shader invocations can be
particularly frequent during traversal. Enhancements are described
for hybrid MIMD ray tracing processors to significantly reduce the
overhead of communication between the cores/EUs 4001 and
traversal/intersection units 4005. This may be particularly
beneficial when finding the k-closest intersections and
implementation of programmable intersection shaders. Note, however,
that the techniques described here are not limited to any
particular processing scenario.
[0460] A summary of the high-level costs of the ray tracing context
switch between the cores/EUs 4001 and fixed function
traversal/intersection unit 4005 is provided below. Most of the
performance overhead is caused by these two context switches every
time when the shader invocation is necessary during single-ray
traversal.
[0461] Each SIMD/SIMT lane that launches a ray generates a spawn
message to the traversal/intersection unit 4005 associated with a
BVH to traverse. The data (ray traversal context) is relayed to the
traversal/intersection unit 4005 via the spawn message and (cached)
memory. When the traversal/intersection unit 4005 is ready to
assign a new hardware thread to the spawn message it loads the
traversal state and performs traversal on the BVH. There is also a
setup cost that needs to be performed before first traversal step
on the BVH.
[0462] FIG. 45 illustrates an operational flow of a programmable
ray tracing pipeline. The shaded elements including traversal 4502
and intersection 4503 may be implemented in fixed function
circuitry while the remaining elements may be implemented with
programmable cores/execution units.
[0463] A primary ray shader 4501 sends work to the traversal
circuitry at 4502 which traverses the current ray(s) through the
BVH (or other acceleration structure). When a leaf node is reached,
the traversal circuitry calls the intersection circuitry at 4503
which, upon identifying a ray-triangle intersection, invokes an any
hit shader at 4504 (which may provide results back to the traversal
circuitry as indicated).
[0464] Alternatively, the traversal may be terminated prior to
reaching a leaf node and a closest hit shader invoked at 4507 (if a
hit was recorded) or a miss shader at 4506 (in the event of a
miss).
[0465] As indicated at 4505, an intersection shader may be invoked
if the traversal circuitry reaches a custom primitive leaf node. A
custom primitive may be any non-triangle primitive such as a
polygon or a polyhedra (e.g., tetrahedrons, voxels, hexahedrons,
wedges, pyramids, or other "unstructured" volume). The intersection
shader 4505 identifies any intersections between the ray and custom
primitive to the any hit shader 4504 which implements any hit
processing.
[0466] When hardware traversal 4502 reaches a programmable stage,
the traversal/intersection unit 4005 may generate a shader dispatch
message to a relevant shader 4505-4507, which corresponds to a
single SIMD lane of the execution unit(s) used to execute the
shader. Since dispatches occur in an arbitrary order of rays, and
they are divergent in the programs called, the sorting unit 4008
may accumulate multiple dispatch calls to extract coherent SIMD
batches. The updated traversal state and the optional shader
arguments may be written into memory 2511 by the
traversal/intersection unit 4005.
[0467] In the k-nearest intersection problem, a closest hit shader
4507 is executed for the first k intersections. In the conventional
way this would mean ending ray traversal upon finding the closest
intersection, invoking a hit-shader, and spawning a new ray from
the hit shader to find the next closest intersection (with the ray
origin offset, so the same intersection will not occur again). It
is easy to see that this implementation would require k ray spawns
for a single ray. Another implementation operates with any-hit
shaders 4504, invoked for all intersections and maintaining a
global list of nearest intersections, using an insertion sort
operation. The main problem with this approach is that there is no
upper bound of any-hit shader invocations.
[0468] As mentioned, an intersection shader 4505 may be invoked on
non-triangle (custom) primitives. Depending on the result of the
intersection test and the traversal state (pending node and
primitive intersections), the traversal of the same ray may
continue after the execution of the intersection shader 4505.
Therefore finding the closest hit may require several roundtrips to
the execution unit.
[0469] A focus can also be put on the reduction of SIMD-MIMD
context switches for intersection shaders 4505 and hit shaders
4504, 4507 through changes to the traversal hardware and the shader
scheduling model. First, the ray traversal circuitry 4005 defers
shader invocations by accumulating multiple potential invocations
and dispatching them in a larger batch. In addition, certain
invocations that turn out to be unnecessary may be culled at this
stage. Furthermore, the shader scheduler 4007 may aggregate
multiple shader invocations from the same traversal context into a
single SIMD batch, which results in a single ray spawn message. In
one exemplary implementation, the traversal hardware 4005 suspends
the traversal thread and waits for the results of multiple shader
invocations. This mode of operation is referred to herein as
"speculative" shader execution because it allows the dispatch of
multiple shaders, some of which may not be called when using
sequential invocations.
[0470] FIG. 46A illustrates an example in which the traversal
operation encounters multiple custom primitives 4650 in a subtree
and FIG. 46B illustrates how this can be resolved with three
intersection dispatch cycles C1-C3. In particular, the scheduler
4007 may require three cycles to submit the work to the SIMD
processor 4001 and the traversal circuitry 4005 requires three
cycles to provide the results to the sorting unit 4008. The
traversal state 4601 required by the traversal circuitry 4005 may
be stored in a memory such as a local cache (e.g., an L1 cache
and/or L2 cache).
A. Deferred Ray Tracing Shader Invocations
[0471] The manner in which the hardware traversal state 4601 is
managed to allow the accumulation of multiple potential
intersection or hit invocations in a list can also be modified. At
a given time during traversal each entry in the list may be used to
generate a shader invocation. For example, the k-nearest
intersection points can be accumulated on the traversal hardware
4005 and/or in the traversal state 4601 in memory, and hit shaders
can be invoked for each element if the traversal is complete. For
hit shaders, multiple potential intersections may be accumulated
for a subtree in the BVH.
[0472] For the nearest-k use case the benefit of this approach is
that instead of k-1 roundtrips to the SIMD core/EU 4001 and k-1 new
ray spawn messages, all hit shaders are invoked from the same
traversal thread during a single traversal operation on the
traversal circuitry 4005. A challenge for potential implementations
is that it is not trivial to guarantee the execution order of hit
shaders (the standard "roundtrip" approach guarantees that the hit
shader of the closest intersection is executed first, etc.). This
may be addressed by either the synchronization of the hit shaders
or the relaxation of the ordering.
[0473] For the intersection shader use case the traversal circuitry
4005 does not know in advance whether a given shader would return a
positive intersection test. However, it is possible to
speculatively execute multiple intersection shaders and if at least
one returns a positive hit result, it is merged into the global
nearest hit. Specific implementations need to find an optimal
number of deferred intersection tests to reduce the number of
dispatch calls but avoid calling too many redundant intersection
shaders.
B. Aggregate Shader Invocations from the Traversal Circuitry
[0474] When dispatching multiple shaders from the same ray spawn on
the traversal circuitry 4005, branches in the flow of the ray
traversal algorithm may be created. This may be problematic for
intersection shaders because the rest of the BVH traversal depend
on the result of all dispatched intersection tests. This means that
a synchronization operation is necessary to wait for the result of
the shader invocations, which can be challenging on asynchronous
hardware.
[0475] Two points of merging the results of the shader calls may
be: the SIMD processor 4001, and the traversal circuitry 4005. With
respect to the SIMD processor 4001, multiple shaders can
synchronize and aggregate their results using standard programming
models. One relatively simple way to do this is to use global
atomics and aggregate results in a shared data structure in memory,
where intersection results of multiple shaders could be stored.
Then the last shader can resolve the data structure and call back
the traversal circuitry 4005 to continue the traversal.
[0476] A more efficient approach may also be implemented which
limits the execution of multiple shader invocations to lanes of the
same SIMD thread on the SIMD processor 4001. The intersection tests
are then locally reduced using SIMD/SIMT reduction operations
(rather than relying on global atomics). This implementation may
rely on new circuitry within the sorting unit 4008 to let a small
batch of shader invocations stay in the same SIMD batch.
[0477] The execution of the traversal thread may further be
suspended on the traversal circuitry 4005. Using the conventional
execution model, when a shader is dispatched during traversal, the
traversal thread is terminated and the ray traversal state is saved
to memory to allow the execution of other ray spawn commands while
the execution units 4001 process the shaders. If the traversal
thread is merely suspended, the traversal state does not need to be
stored and can wait for each shader result separately. This
implementation may include circuitry to avoid deadlocks and provide
sufficient hardware utilization.
[0478] FIGS. 47-48 illustrate examples of a deferred model which
invokes a single shader invocation on the SIMD cores/execution
units 4001 with three shaders 4701. When preserved, all
intersection tests are evaluated within the same SIMD/SIMT group.
Consequently, the nearest intersection can also be computed on the
programmable cores/execution units 4001.
[0479] As mentioned, all or a portion of the shader aggregation
and/or deferral may be performed by the traversal/intersection
circuitry 4005 and/or the core/EU scheduler 4007. FIG. 47
illustrates how shader deferral/aggregator circuitry 4706 within
the scheduler 4007 can defer scheduling of shaders associated with
a particular SIMD/SIMT thread/lane until a specified triggering
event has occurred. Upon detecting the triggering event, the
scheduler 4007 dispatches the multiple aggregated shaders in a
single SIMD/SIMT batch to the cores/EUs 4001.
[0480] FIG. 48 illustrates how shader deferral/aggregator circuitry
4805 within the traversal/intersection circuitry 4005 can defer
scheduling of shaders associated with a particular SIMD thread/lane
until a specified triggering event has occurred. Upon detecting the
triggering event, the traversal/intersection circuitry 4005 submits
the aggregated shaders to the sorting unit 4008 in a single
SIMD/SIMT batch.
[0481] Note, however, that the shader deferral and aggregation
techniques may be implemented within various other components such
as the sorting unit 4008 or may be distributed across multiple
components. For example, the traversal/intersection circuitry 4005
may perform a first set of shader aggregation operations and the
scheduler 4007 may perform a second set of shader aggregation
operations to ensure that shaders for a SIMD thread are scheduled
efficiently on the cores/EUs 4001.
[0482] The "triggering event" to cause the aggregated shaders to be
dispatched to the cores/EUs may be a processing event such as a
particular number of accumulated shaders or a minimum latency
associated with a particular thread. Alternatively, or in addition,
the triggering event may be a temporal event such as a certain
duration from the deferral of the first shader or a particular
number of processor cycles. Other variables such as the current
workload on the cores/EUs 4001 and the traversal/intersection unit
4005 may also be evaluated by the scheduler 4007 to determine when
to dispatch the SIMD/SIMT batch of shaders.
[0483] Different embodiments of the invention may be implemented
using different combinations of the above approaches, based on the
particular system architecture being used and the requirements of
the application.
Ray Tracing Instructions
[0484] The ray tracing instructions described below are included in
an instruction set architecture (ISA) supported the CPU 3199 and/or
GPU 3105. If executed by the CPU, the single instruction multiple
data (SIMD) instructions may utilize vector/packed source and
destination registers to perform the described operations and may
be decoded and executed by a CPU core. If executed by a GPU 3105,
the instructions may be executed by graphics cores 3130. For
example, any of the execution units (EUs) 4001 described above may
execute the instructions. Alternatively, or in addition, the
instructions may be executed by execution circuitry on the ray
tracing cores 3150 and/or tensor cores tensor cores 3140.
[0485] FIG. 49 illustrates an architecture for executing the ray
tracing instructions described below. The illustrated architecture
may be integrated within one or more of the cores 3130, 3140, 3150
described above (see, e.g., FIG. 31 and associated text) of may be
included in a different processor architecture.
[0486] In operation, an instruction fetch unit 4903 fetches ray
tracing instructions 4900 from memory 3198 and a decoder 4995
decodes the instructions. In one implementation the decoder 4995
decodes instructions to generate executable operations (e.g.,
microoperations or uops in a microcoded core). Alternatively, some
or all of the ray tracing instructions 4900 may be executed without
decoding and, as such a decoder 4904 is not required.
[0487] In either implementation, a scheduler/dispatcher 4905
schedules and dispatches the instructions (or operations) across a
set of functional units (FUs) 4910-4912. The illustrated
implementation includes a vector FU 4910 for executing single
instruction multiple data (SIMD) instructions which operate
concurrently on multiple packed data elements stored in vector
registers 4915 and a scalar FU 4911 for operating on scalar values
stored in one or more scalar registers 4916. An optional ray
tracing FU 4912 may operate on packed data values stored in the
vector registers 4915 and/or scalar values stored in the scalar
registers 4916. In an implementation without a dedicated FU 4912,
the vector FU 4910 and possibly the scalar FU 4911 may perform the
ray tracing instructions described below.
[0488] The various FUs 4910-4912 access ray tracing data 4902
(e.g., traversal/intersection data) needed to execute the ray
tracing instructions 4900 from the vector registers 4915, scalar
register 4916 and/or the local cache subsystem 4908 (e.g., a L1
cache). The FUs 4910-4912 may also perform accesses to memory 3198
via load and store operations, and the cache subsystem 4908 may
operate independently to cache the data locally.
[0489] While the ray tracing instructions may be used to increase
performance for ray traversal/intersection and BVH builds, they may
also be applicable to other areas such as high performance
computing (HPC) and general purpose GPU (GPGPU)
implementations.
[0490] In the below descriptions, the term double word is sometimes
abbreviated dw and unsigned byte is abbreviated ub. In addition,
the source and destination registers referred to below (e.g., src0,
src1, dest, etc) may refer to vector registers 4915 or in some
cases a combination of vector registers 4915 and scalar registers
4916. Typically, if a source or destination value used by an
instruction includes packed data elements (e.g., where a source or
destination stores N data elements), vector registers 4915 are
used. Other values may use scalar registers 4916 or vector
registers 4915.
Dequantize
[0491] One example of the Dequantize instruction "dequantizes"
previously quantized values. By way of example, in a ray tracing
implementation, certain BVH subtrees may be quantized to reduce
storage and bandwidth requirements. The dequantize instruction may
take the form dequantize dest src0 src1 src2 where source register
src0 stores N unsigned bytes, source register src1 stores 1
unsigned byte, source register src2 stores 1 floating point value,
and destination register dest stores N floating point values. All
of these registers may be vector registers 4915. Alternatively,
src0 and dest may be vector registers 4915 and src 1 and src2 may
be scalar registers 4916.
[0492] The following code sequence defines one particular
implementation of the dequantize instruction:
TABLE-US-00006 for (int i = 0; i < SIMD_WIDTH) { if
(execMask[i]) { dst[i] = src2[i] +
Idexp(convert_to_float(src0[1]),src1); } }
In this example, Idexp multiplies a double precision floating point
value by a specified integral power of two (i.e., Idexp(x,
exp)=x*2.sup.exp). In the above code, if the execution mask value
associated with the current SIMD data element (execMask[i])) is set
to 1, then the SIMD data element at location i in src0 is converted
to a floating point value and multiplied by the integral power of
the value in src1 (2.sup.src1 value) and this value is added to the
corresponding SIMD data element in src2.
Selective Min or Max
[0493] A selective min or max instruction may perform either a min
or a max operation per lane (i.e., returning the minimum or maximum
of a set of values), as indicated by a bit in a bitmask. The
bitmask may utilize the vector registers 4915, scalar registers
4916, or a separate set of mask registers (not shown). The
following code sequence defines one particular implementation of
the min/max instruction: sel_min_max dest src0 src1 src2, where
src0 stores N doublewords, src1 stores N doublewords, src2 stores
one doubleword, and the destination register stores N
doublewords.
[0494] The following code sequence defines one particular
implementation of the selective min/max instruction:
TABLE-US-00007 for (int i = 0; i < SIMD_WIDTH) { if
(execMask[i]) { dst[i] = (1 << i) & src2 ?
min(src0[i],src1[i]) : max(src0[i],src1[i]); } }
In this example, the value of (1<i) & src2 (a 1 left-shifted
by i ANDed with src2) is used to select either the minimum of the
i.sup.th data element in src0 and src1 or the maximum of the
i.sup.th data element in src0 and src1. The operation is performed
for the i.sup.th data element only if the execution mask value
associated with the current SIMD data element (execMask[i])) is set
to 1.
Shuffle Index Instruction
[0495] A shuffle index instruction can copy any set of input lanes
to the output lanes. For a SIMD width of 32, this instruction can
be executed at a lower throughput. This instruction takes the form:
shuffle_index dest src0 src1 <optional flag>, where src0
stores N doublewords, src1 stores N unsigned bytes (i.e., the index
value), and dest stores N doublewords.
[0496] The following code sequence defines one particular
implementation of the shuffle index instruction:
TABLE-US-00008 for (int i = 0; i < SIMD_WIDTH) { uint8_t srcLane
= src1.index[i]; if (execMask[i]) { bool invalidLane = srcLane <
0 | | srcLane >= SIMD_WIDTH | | !execMask[srcLaneMod]; if (FLAG)
{ invalidLane |= flag[srcLaneMod]; } if (invalidLane) { dst[i] =
src0[i]; } else { dst[i] = src0[srcLane]; } } }
[0497] In the above code, the index in src1 identifies the current
lane. If the i.sup.th value in the execution mask is set to 1, then
a check is performed to ensure that the source lane is within the
range of 0 to the SIMD width. If so, then flag is set (srcLaneMod)
and data element i of the destination is set equal to data element
i of src0. If the lane is within range (i.e., is valid), then the
index value from src1 (srcLane0) is used as an index into src0
(dst[i]=src0[srcLane]).
Immediate Shuffle Up/Dn/XOR Instruction
[0498] An immediate shuffle instruction may shuffle input data
elements/lanes based on an immediate of the instruction. The
immediate may specify shifting the input lanes by 1, 2, 4, 8, or 16
positions, based on the value of the immediate. Optionally, an
additional scalar source register can be specified as a fill value.
When the source lane index is invalid, the fill value (if provided)
is stored to the data element location in the destination. If no
fill value is provided, the data element location is set to all
0.
[0499] A flag register may be used as a source mask. If the flag
bit for a source lane is set to 1, the source lane may be marked as
invalid and the instruction may proceed.
[0500] The following are examples of different implementations of
the immediate shuffle instruction:
TABLE-US-00009 shuffle_<up/dn/xor>_<1/2/4/8/16> dest
src0 <optional src1> <optional flag>
shuffle_<up/dn/xor>_<1/2/4/8/16> dest src0 <optional
src1> <optional flag>
[0501] In this implementation, src0 stores N doublewords, src1
stores one doubleword for the fill value (if present), and dest
stores N doublewords comprising the result.
[0502] The following code sequence defines one particular
implementation of the immediate shuffle instruction:
TABLE-US-00010 for (int i = 0; i < SIMD_WIDTH) { int8_t srcLane;
switch(SHUFFLE_TYPE) { case UP: srcLane = i - SHIFT; case DN:
srcLane = i + SHIFT; case XOR: srcLane = i {circumflex over ( )}
SHIFT; } if (execMask[i]) { bool invalidLane = srcLane < 0 | |
srcLane >= SIMD_WIDTH | | !execMask[srcLane]; if (FLAG) {
invalidLane |= flag[srcLane]; } if (invalidLane) { if (SRC1) dst[i]
= src1; else dst[i] = 0; } else { dst[i] = src0[srcLane]; } } }
[0503] Here the input data elements/lanes are shifted by 1, 2, 4,
8, or 16 positions, based on the value of the immediate. The
register src1 is an additional scalar source register which is used
as a fill value which is stored to the data element location in the
destination when the source lane index is invalid. If no fill value
is provided and the source lane index is invalid, the data element
location in the destination is set to 0s. The flag register (FLAG)
is used as a source mask. If the flag bit for a source lane is set
to 1, the source lane is marked as invalid and the instruction
proceeds as described above.
Indirect Shuffle Up/Dn/XOR Instruction
[0504] The indirect shuffle instruction has a source operand (src1)
that controls the mapping from source lanes to destination lanes.
The indirect shuffle instruction may take the form: [0505]
shuffle_<up/dn/xor>dest src0 src1 <optional flag> where
src0 stores N doublewords, src1 stores 1 doubleword, and dest
stores N doublewords.
[0506] The following code sequence defines one particular
implementation of the immediate shuffle instruction:
TABLE-US-00011 for (int i = 0; i < SIMD_WIDTH) { int8_t srcLane;
switch(SHUFFLE_TYPE) { case UP: srcLane = i - src1; case DN:
srcLane = i + src1; case XOR: srcLane = i {circumflex over ( )}
src1; } if (execMask[i]) { bool invalidLane = srcLane < 0 | |
srcLane >= SIMD_WIDTH | | !execMask[srcLane]; if (FLAG) {
invalidLane |= flag[srcLane]; } if (invalidLane) { dst[i] = 0; }
else { dst[i] = src0[srcLane]; } } }
[0507] Thus, the indirect shuffle instruction operates in a similar
manner to the immediate shuffle instruction described above, but
the mapping of source lanes to destination lanes is controlled by
the source register src1 rather than the immediate.
Cross Lane Min/Max Instruction
[0508] A cross lane minimum/maximum instruction may be supported
for float and integer data types. The cross lane minimum
instruction may take the form lane_min dest src0 and the cross lane
maximum instruction may take the form lane_max dest src0, where
src0 stores N doublewords and dest stores 1 doubleword.
[0509] By way of example, the following code sequence defines one
particular implementation of the cross lane minimum:
TABLE-US-00012 dst = src[0]; for (int i = 1; i < SIMD_WIDTH) {
if (execMask[i]) { dst = min(dst, src[i]); } }
[0510] In this example, the doubleword value in data element
position i of the source register is compared with the data element
in the destination register and the minimum of the two values is
copied to the destination register. The cross lane maximum
instruction operates in substantially the same manner, the only
difference being that the maximum of the data element in position i
and the destination value is selected.
Cross Lane Min/Max Index Instruction
[0511] A cross lane minimum index instruction may take the form
lane_min_index dest src0 and the cross lane maximum index
instruction may take the form lane_max_index dest src0, where src0
stores N doublewords and dest stores 1 doubleword.
[0512] By way of example, the following code sequence defines one
particular implementation of the cross lane minimum index
instruction:
TABLE-US-00013 dst_index = 0; tmp = src[0] for (int i = 1; i <
SIMD_WIDTH) { if (src[i] < tmp && execMask[i]) { tmp =
src[i]; dst_index = i; } }
In this example, the destination index is incremented from 0 to
SIMD width, spanning the destination register. If the execution
mask bit is set, then the data element at position i in the source
register is copied to a temporary storage location (tmp) and the
destination index is set to data element position i.
Cross Lane Sorting Network Instruction
[0513] A cross-lane sorting network instruction may sort all N
input elements using an N-wide (stable) sorting network, either in
ascending order (sortnet_min) or in descending order (sortnet_max).
The min/max versions of the instruction may take the forms
sortnet_min dest src0 and sortnet_max dest src0, respectively. In
one implementation, src0 and dest store N doublewords. The min/max
sorting is performed on the N doublewords of src0, and the
ascending ordered elements (for min) or descending ordered elements
(for max) are stored in dest in their respective sorted orders. One
example of a code sequence defining the instruction is:
dst=apply_N_wide_sorting_network_min/max(src0).
Cross Lane Sorting Network Index Instruction
[0514] A cross-lane sorting network index instruction may sort all
N input elements using an N-wide (stable) sorting network but
returns the permute index, either in ascending order (sortnet_min)
or in descending order (sortnet_max). The min/max versions of the
instruction may take the forms sortnet_min_index dest src0 and
sortnet_max_index dest src0 where src0 and dest each store N
doublewords. One example of a code sequence defining the
instruction is
dst=apply_N_wide_sorting_network_min/max_index(src0).
[0515] A method for executing any of the above instructions is
illustrated in FIG. 50. The method may be implemented on the
specific processor architectures described above, but is not
limited to any particular processor or system architecture.
[0516] At 5001 instructions of a primary graphics thread are
executed on processor cores. This may include, for example, any of
the cores described above (e.g., graphics cores 3130). When ray
tracing work is reached within the primary graphics thread,
determined at 5002, the ray tracing instructions are offloaded to
the ray tracing execution circuitry which may be in the form of a
functional unit (FU) such as described above with respect to FIG.
49 or which may be in a dedicated ray tracing core 3150 as
described with respect to FIG. 31.
[0517] At 5003, the ray tracing instructions are decoded are
fetched from memory and, at 5005, the instructions are decoded into
executable operations (e.g., in an embodiment which requires a
decoder). At 5004 the ray tracing instructions are scheduled and
dispatched for execution by ray tracing circuitry. At 5005 the ray
tracing instructions are executed by the ray tracing circuitry. For
example, the instructions may be dispatched and executed on the FUs
described above (e.g., vector FU 4910, ray tracing FU 4912, etc)
and/or the graphics cores 3130 or ray tracing cores 3150.
[0518] When execution is complete for a ray tracing instruction,
the results are stored at 5006 (e.g., stored back to the memory
3198) and at 5007 the primary graphics thread is notified. At 5008,
the ray tracing results are processed within the context of the
primary thread (e.g., read from memory and integrated into graphics
rendering results).
[0519] In embodiments, the term "engine" or "module" or "logic" may
refer to, be part of, or include an application specific integrated
circuit (ASIC), an electronic circuit, a processor (shared,
dedicated, or group), and/or memory (shared, dedicated, or group)
that execute one or more software or firmware programs, a
combinational logic circuit, and/or other suitable components that
provide the described functionality. In embodiments, an engine,
module, or logic may be implemented in firmware, hardware,
software, or any combination of firmware, hardware, and
software.
Apparatus and Method for Asynchronous Ray Tracing
[0520] Embodiments of the invention include a combination of fixed
function acceleration circuitry and general purpose processing
circuitry to perform ray tracing. For example, certain operations
related to ray traversal of a bounding volume hierarchy (BVH) and
intersection testing may be performed by the fixed function
acceleration circuitry, while a plurality of execution circuits
execute various forms of ray tracing shaders (e.g., any hit
shaders, intersection shaders, miss shaders, etc). One embodiment
includes dual high-bandwidth storage banks comprising a plurality
of entries for storing rays and corresponding dual stacks for
storing BVH nodes. In this embodiment, the traversal circuitry
alternates between the dual ray banks and stacks to process a ray
on each clock cycle. In addition, one embodiment includes priority
selection circuitry/logic which distinguishes between internal
nodes, non-internal nodes, and primitives and uses this information
to intelligently prioritize processing of the BVH nodes and the
primitives bounded by the BVH nodes.
[0521] One particular embodiment reduces the high speed memory
required for traversal using a short stack to store a limited
number of BVH nodes during traversal operations. This embodiment
includes stack management circuitry/logic to efficiently push and
pop entries to and from the short stack to ensure that the required
BVH nodes are available. In addition, traversal operations are
tracked by performing updates to a tracking data structure. When
the traversal circuitry/logic is paused, it can consult the
tracking data structure to begin traversal operations at the same
location within the BVH where it left off. and the tracking data
maintained in a data structure tracking is performed so that the
traversal circuitry/logic can restart.
[0522] FIG. 51 illustrates one embodiment comprising shader
execution circuitry 4000 for executing shader program code and
processing associated ray tracing data 4902 (e.g., BVH node data
and ray data), ray tracing acceleration circuitry 5110 for
performing traversal and intersection operations, and a memory 3198
for storing program code and associated data processed by the RT
acceleration circuitry 5110 and shader execution circuitry
4000.
[0523] In one embodiment, the shader execution circuitry 4000
includes a plurality of cores/execution units 4001 which execute
shader program code to perform various forms of data-parallel
operations. For example, in one embodiment, the cores/execution
units 4001 can execute a single instruction across multiple lanes,
where each instance of the instruction operates on data stored in a
different lane. In a SIMT implementation, for example, each
instance of the instruction is associated with a different thread.
During execution, an L1 cache stores certain ray tracing data for
efficient access (e.g., recently or frequently accessed data).
[0524] A set of primary rays may be dispatched to the scheduler
4007, which schedules work to shaders executed by the cores/EUs
4001. The cores/EUs 4001 may be ray tracing cores 3150, graphics
cores 3130, CPU cores 3199 or other types of circuitry capable of
executing shader program code. One or more primary ray shaders 5101
process the primary rays and spawn additional work to be performed
by ray tracing acceleration circuitry 5110 and/or the cores/EUs
4001 (e.g., to be executed by one or more child shaders). New work
spawned by the primary ray shader 5101 or other shaders executed by
the cores/EUs 4001 may be distributed to sorting circuitry 4008
which sorts the rays into groups or bins as described herein (e.g.,
grouping rays with similar characteristics). The scheduler 4007
then schedules the new work on the cores/EUs 4001.
[0525] Other shaders which may be executed include any hit shaders
4514 and closest hit shaders 4507 which process hit results as
described above (e.g., identifying any hit or the closest hit for a
given ray, respectively). A miss shader 4506 processes ray misses
(e.g., where a ray does not intersect the node/primitive). As
mentioned, the various shaders can be referenced using a shader
record which may include one or more pointers, vendor-specific
metadata, and global arguments. In one embodiment, shader records
are identified by shader record identifiers (SRI). In one
embodiment, each executing instance of a shader is associated with
a call stack 5203 which stores arguments passed between a parent
shader and child shader. Call stacks 5121 may also store references
to continuation functions that are executed when a call
returns.
[0526] Ray traversal circuitry 5102 traverses each ray through
nodes of a BVH, working down the hierarchy of the BVH (e.g.,
through parent nodes, child nodes, and leaf nodes) to identify
nodes/primitives traversed by the ray. Ray-BVH intersection
circuitry 5103 performs intersection testing of rays, determining
hit points on primitives, and generates results in response to the
hits. The traversal circuitry 5102 and intersection circuitry 5103
may retrieve work from the one or more call stacks 5121. Within the
ray tracing acceleration circuitry 5110, call stacks 5121 and
associated ray tracing data 4902 may be stored within a local ray
tracing cache (RTC) 5107 or other local storage device for
efficient access by the traversal circuitry 5102 and intersection
circuitry 5103. One particular embodiment described below includes
high-bandwidth ray banks (see, e.g., FIG. 52A).
[0527] The ray tracing acceleration circuitry 5110 may be a variant
of the various traversal/intersection circuits described herein
including ray-BVH traversal/intersection circuit 4005, traversal
circuit 4502 and intersection circuit 4503, and ray tracing cores
3150. The ray tracing acceleration circuitry 5110 may be used in
place of the ray-BVH traversal/intersection circuit 4005, traversal
circuit 4502 and intersection circuit 4503, and ray tracing cores
3150 or any other circuitry/logic for processing BVH stacks and/or
performing traversal/intersection. Therefore, the disclosure of any
features in combination with the ray-BVH traversal/intersection
circuit 4005, traversal circuit 4502 and intersection circuit 4503,
and ray tracing cores 3150 described herein also discloses a
corresponding combination with the ray tracing acceleration
circuitry 5110, but is not limited to such.
[0528] Referring to FIG. 52A, one embodiment of the ray traversal
circuitry 5102 includes first and second ray storage banks, 5201
and 5202, respectively, where each bank comprises a plurality of
entries for storing a corresponding plurality of incoming rays 5206
loaded from memory. Corresponding first and second stacks, 5203 and
5204, respectively, comprise selected BVH node data 5290-5291 read
from memory and stored locally for processing. As described herein,
in one embodiment, the stacks 5203-5204 are "short" stacks
comprising a limited number of entries for storing BVH node data
(e.g., six entries in one embodiment). While illustrated separately
from the ray banks 5201-5202, the stacks 5203-5204 may also be
maintained within the corresponding ray banks 5201-5202.
Alternatively, the stacks 5203-5204 may be stored in a separate
local memory or cache.
[0529] One embodiment of the traversal processing circuitry 5210
alternates between the two banks 5201-5202 and stacks 5203-5204
when selecting the next ray and node to process (e.g., in a
ping-pong manner). For example, the traversal processing circuitry
5210 may select a new ray/BVH node from an alternate ray bank/stack
on each clock cycle, thereby ensuring highly efficient operation.
It should be noted, however, this specific arrangement is not
necessary for complying with the underlying principles of the
invention.
[0530] In one embodiment, a ray allocator 5205 balances the entry
of incoming rays 5206 into the first and second memory banks
5201-5202, respectively, based on current relative values of a set
of bank allocation counters 5220. In one embodiment, the bank
allocation counters 5220 maintain a count of the number of
untraversed rays in each of the first and second memory banks
5201-5202. For example, a first bank allocation counter may be
incremented when the ray allocator 5205 adds a new ray to the first
bank 5201 and decremented when a ray is processed from the first
bank 5201. Similarly, the second bank allocation counter may be
incremented when the ray allocator 5205 adds a new ray to the
second bank 5201 and decremented when a ray is processed from the
second bank 5201.
[0531] In one embodiment, the ray allocator 5205 allocates the
current ray to a bank associated with the smaller counter value. If
the two counters are equal, the ray allocator 5205 may select
either bank or may select a different bank from the one selected
the last time the counters were equal. In one embodiment, each ray
is stored in one entry of one of the banks 5201-5202 and each bank
comprises 32 entries for storing up to 32 rays. However, the
underlying principles of the invention are not limited to these
details.
[0532] FIG. 52B illustrates four processes 5251-5254 executed in
one embodiment to manage the ray storage banks 5201-5202 and stacks
5203-5204. In one embodiment, the four processes 5251-5254 are
different implementations or configurations of a common set of
program code (sometimes referred to herein as "TraceRay"). The
Initial process 5251 may be executed to read the ray 5261 and
perform a new top-down traversal of a BVH, starting from the root
node. The Alloc function modifies control bits and launches
corresponding read requests to the ray tracing stack. In
particular, to allocate the new entry, Alloc sets the valid (VLD)
bit and resets the evict ready (Evict_Rdy) bit. In the bank entry
for the ray, the data present (DP) bit and the dirty bit are reset.
The DP bit in the corresponding stack entry is set. For the
corresponding Hitinfo, the DP bit is set and the dirty bit is
reset. The DP bit and the shader record identifier (SRI) DP bit
associated with the node data are reset.
[0533] The instance process 5252 performs traversal within one of
the nodes of the BVH (other than the root node) and reads the ray
and prior committed hit 5262. In one embodiment, when one of the
hit shaders identifies a hit between the ray and a primitive, then
the commit process 5253 is executed to commit results, reading the
ray, the potential hit, and the stack 5263. Alternatively, the
continue process 5254 is executed to continue traversal of the ray,
reading the ray, the committed hit, and the stack 5264.
[0534] In various circumstances, the traversal circuitry 5002 must
pause traversal operations and save the current ray and associated
BVH nodes, such as when a shader is required to perform a sequence
of operations. For example, if a non-opaque object is hit or a
procedural texture, the traversal circuitry 5002 saves the stack
5203-5204 to memory and executes the required shader. Once the
shader has completed processing the hit (or other data), the
traversal circuitry 5002 restores the state of the ray banks
5201-5202 and stacks 5203-5204 from memory.
[0535] In one embodiment, a traversal/stack tracker 5248
continually monitors traversal and stack operations and stores
restart data in a tracking array 5249. For example, if the
traversal circuitry 5002 has already traversed nodes N, N0, N1, N2,
and N00, and generated results, then the traversal/stack tracker
5248 will update the tracking array to indicate that traversal of
these nodes has completed and/or to indicate the next node to be
processed from the stack. When the traversal circuitry 5002 is
restarted, it reads the restart data from the tracking array 5249
so that it may restart traversal at the correct stage, without
re-traversing any of the BVH nodes (and wasting cycles). The
restart data stored in the tracking array 5249 is sometimes
referred to as the "restart trail" or "RST."
[0536] As indicated in FIG. 52B, the various TraceRay processes
5251-5254 manage allocation into and out of the ray storage banks
5201-5202 via one or more functions. As illustrated for the initial
process 5251, an Alloc function sets the valid bit (VLD) in a
storage bank entry (indicating that the entry now contains a valid
ray) and resets (Rst) the eviction ready flag (indicating that the
ray data should not be evicted). The Ray function stores the ray in
the selected entry and resets the data present (DP) bit (indicating
that ray data is stored in the entry) and the dirty bit (indicating
that the data has not been modified). Upon reading the ray from the
storage bank, the Stack function sets the DP bit and retrieves the
relevant BVH node from the stack (e.g., the root node in the case
of the initial process 5251 and another node in the case of the
instance process 5252). The HitInfo function resets the dirty bit
and sets the DP bit for the initial function 5251 or resets it for
all other functions. In one embodiment, Hitinfo produces data
reflecting a ray hit. The Node function resets the DP bit and the
SRI (shader record identifier) DP which is the DP for Shader Record
Identifier. One embodiment performs a Kernel Start Pointer (KSP)
lookup to ensure that KSP is not equal to zero. If it is, then
different handling is implemented for non-opaque Quads.
[0537] In one embodiment, once a ray entry has been allocated in
one of the storage banks 5201-5202 a fetch is performed to retrieve
the node data (and potentially other data) from the stack
associated with the ray. In one embodiment, a stack is maintained
for each ray, comprising the working set of data for the current
node through which the ray is traversed.
[0538] When moving to the next level in the BVH (e.g., upon
determining that the ray intersects a parent node), the child nodes
are sorted and pushed on the stack 5203-5204. The child nodes are
popped off the stack sequentially and processed individually to
identify child nodes which the ray traverses (traversal "hits"). In
one embodiment, the stack is stored out to memory or a local
cache/storage whenever there is a handoff between the RT
acceleration circuitry 5110 and the shaders 4504, 4506, 4507, 5101,
5105.
[0539] When a leaf node comprising a quad or triangle (or other
primitive type) is identified by the traversal circuitry 5102, it
passes this information to the intersection circuitry 5103 which
performs an intersection test on the quad or triangle,
respectively. If the primitive is not a quad or triangle then, in
one implementation, the traversal circuitry terminates traversal
and passes control back to the closest hit shader 4507 (if a hit is
detected) or the miss shader 4506 (if no hit is detected). In an
implementation in which the intersection circuitry 5103 is designed
to perform intersections for a variety of primitives in addition to
quads and triangles (e.g., lines, arcs, circles, etc), then the
traversal circuitry 5102 will forward leaf nodes for these
primitives to the intersection circuitry 5103.
[0540] In one embodiment, when a hardware or software component
generates a read request to memory 3198 or cache, a 16-bit tag is
used to provide information about the data type and requestor. For
example, a two-bit code may specify whether the request is for a
ray, stack data, hit data, node data from the BVH, or any other
type of data. When the ray, stack, and Hitinfo has been returned
from memory, the ray is traversed through one or more BVH nodes and
intersection testing is performed as described above.
[0541] One or more stacks 5203-5204 and rays 5206 are loaded from
memory at different processing stages. For example, the initial
process 5251 and/or instance process 5252 may require a new BVH to
be loaded for traversal. In these circumstances, the stack
5203-5204 may be initialized to the top node (or "root" node) of
the BVH. For a ray continuation 5254 within a BVH, the stack
5203-5204 may be loaded from memory and expanded. Once the stack
5203-5204 has been prepared, node data is fetched from the stack
(an operation sometimes referred to below as Proc_Node_Fetch).
[0542] In one embodiment, node data is fetched by launching
parallel requests for two non-internal (NI) nodes and two internal
nodes. FIG. 53 illustrates one such embodiment in which NI node
priority selection logic (PRISEL) 5311 requests dual NI nodes: a
first NI node 5301 from Bank 0 and a second NI node 5302 from Bank
1. Concurrently, Internal Node PRISEL logic 5312 requests dual
internal nodes: a first node 5303 from Bank 0 and a second node
5304 from Bank 1.
[0543] In one embodiment, NI node priority selection logic (PRISEL)
5311 prioritizes one of the first NI node 5301 and second NI node
5302, storing the prioritized result in the ray tracing cache
(RTC). Similarly, Internal Node PRISEL logic 5312 requests dual
internal nodes, and selects a prioritized result from a first
internal node 5303 and a second internal node 5304.
[0544] Each instance of the priority selection logic 5311-5312
prioritizes one of the non-internal BVH nodes 5301-5302 and one of
the internal BVH nodes 5303-5304 from a different bank if possible.
In one embodiment, only one request is selected from each bank
(e.g., one of requests 5302 and 5304 and one of requests 5301 and
5303). The launch of these requests may also reset the stack data
present (DP) bit, as indicated, so that this entry is not retrieved
in response to a node fetch operation. In one embodiment, for the
instance fetch operation, the ray's data present (DP) bit is reset
when the instance request is sent, and finally set when the ray is
transformed after the node fetch.
[0545] In one embodiment, node_info is written at the launch of
reads and the address/tag is calculated as follows for the reads
requests: [0546] i.
rtt_rtc_rd_addr[47:6]=rt_rayst_ray_ctrl.root_node_ptr[47:6]+curr_stack-
.child_offset; (Note: The Child offset on the node is always with
respect to Current BVH Root Node) [0547] ii.
rtt_rtc_rd_tag[6:0]={RTT_INST, rtt_alloc_entry[5:0]}; [0548] iii.
node.node_info=curr_stack.node_info. In one embodiment, the node
data returned will set the DP bit for the node and the stack.
[0549] The following cases can be distinguished based on the read
tag:
A. Internal Node: This will write to the node B. Instance: This
will update the rt_ray.rt_ray_ctrl for next level BVH (1) and write
the Node Structure. [0550] i.
root_node_ptr=node_return.StartNodePtr [0551] ii.
hitgrp_srbase_ptr=rt_ray_ctrl.hitgrp_srbase_ptr+rt_ray_ctrl.srstride*node-
_return.instancecontributiontohitgrpindex [0552] iii.
hitgrp_sr_stride=rt_ray_ctrl.srstride*rt_ray_ctrl.shade_indx_mult
[0553] iv.
inst_leaf_ptr=rt_ray.rt_ray_ctrl.root_node_ptr+stack.current_node.chi-
ld_offset.fwdarw.Just Logical view, grab and store the node fetch
address during Instance Node fetch request itself [0554] v.
{miss_sr_ptr, shader_indx_mult,
mask}={rt_ray[0].rt_ray_ctrl.miss_sr_ptr, rt_ray[0].rt_ray_ctrl.
shader_indx_mult, rt_ray[0].rt_ray_ctrl.mask} .quadrature. Preserve
BVH[0] [0555] vi.
flag[0]=rt_ray[0].rt_ray_ctrl.flag[0]|(.about.rt_ray[0].rt_ray_ctrl.flag[-
1] & Node_Return.flag[2]);.fwdarw.Either Preserve Opaque via
Ray or Via Instance Flag (only if Ray Flag is not Force Non-Opaque)
[0556] vii. flag[1]=(rt_ray[0].rt_ray_ctrl.flag[1])
(.about.rt_ray[0].rt_ray_ctrl.flag[0] &
Node_Return.flag[3]);.fwdarw.Either Preserve Non Opaque via Ray or
Via Instance Flag (only if Ray Flag is not Force Opaque) [0557]
viii. flag[3:2]=rt_ray[0].rt_ray_ctrl.flag[3:2];.fwdarw.(Accept
FIRST HIT and end Search or Skip Closest Hit Shader) Preserve
BVH[0] [0558] ix. flag[5:4]=Node_Return.flag[0] ? 2'd0:
rt_ray[0].rt_ray_ctrl.flag[5:4];.fwdarw.Triangle Culling is
disabled VIA Instance [0559] x.
flag[8:6]=rt_ray[0].rt_ray_ctrl.flag[8:6];.fwdarw.(Disable
intersection shader, Cull Opaque or Cull Non-Opaque) Preserve
BVH[0] [0560] xi. node.node_ctrl=Not Needed for instance [0561]
xii. node.node_data={'0, node_rtn.obj2world_p, world2obj_vzyx}; C.
Quad: This will update the node as follows [0562] i.
node.node_ctrl={node_rtn.leafDesc.last,
node_rtn.leafDesc.PrimIndex1Delta[15:0],
node_rtn.leafDesc.PrimIndex0[31:0], node_rtn.shader_indx}; [0563]
ii. node.node_data={'0, Quad_mode, J[2:0], V[3:0]};
.fwdarw.Quad_mode=node_rtn.leafDesc.PrimIndex1Delta[15:0] !='0;
[0564] Based on the ray flag, instance flag, and the geometry flag,
the opaque/non-opaque handling table shown in FIG. 55A indicates
the resulting flag to be used when the node data is fetched (opaque
or non-opaque). As indicated in the table, ray flags always take
precedence. Additionally, some of the states are mutually
exclusive. In one embodiment, these are handled in hardware with
the priority of exclusive bits. In one implementation, if
cull_opaque and force_opaque are both set, the associated geometry
will automatically be culled. [0565]
opaque=rt_ray.rt_ray_ctrl.flag[0]|quad.flag[0]; (Note the Ray
Stored per BVH Level is already accounting for the instance Flags)
[0566] nopaque=rt_ray.rt_ray_ctrl.flag[1]|.about.quad.flag[0];
[0567] FIG. 55B is a table showing ray flag handling and exceptions
in accordance with one embodiment. Here the decision to cull is
based on a combination of the ray flag, instance flag, and geometry
flag. [0568] cull_opaque=rt_rayst_ray_ctrl.flag[6] &
(rt_rayst_ray_ctrl.flag[0]|quad.flag[0]); [0569]
cull_nopaque=rt_rayst_ray_ctrl.flag[7] &
(rt_rayst_ray_ctrl.flag[1]|.about.quad.flag[0]); [0570]
cull=cull_opaque|cull_nopaque;
[0571] A mask-based cull may be implemented as follows in one
embodiment: [0572] mask_kill=.about.|(rtc_rtt_rd_rtn.mask &
rtc_rtt_rd_rtn.data.mask);
[0573] FIG. 55C is a table showing final culling in accordance with
one embodiment. The Ray Flag being (cull_opaque and force_opaque)
or (cull_non_opaque and force_non_opaque) are mutually exclusive.
However, in this equation the Ray Flag is also accounting for the
instance flag which can set the opaque/non-opaque. Only Geometry
can be culled whereas both instance and geometry can be masked.
[0574] As illustrated in FIG. 56, in one embodiment, based on the
evaluation of the cull and mask_kill settings described above,
early out is determined at 5601 or 5602 and the result either sent
to node storage at 5603 and/or the stack at 5604.
[0575] Once the node data is ready, box/intersection tests may be
performed. This is accomplished in one embodiment by a process
referred to herein as Ray_Test_Proc which has two underlying
concurrent processes running, one to fill the quad/instance (QI)
and another to perform the box/intersection testing. In one
implementation illustrated in FIG. 57, Ray_Test_Proc launches two
parallel instances of priority selection logic (PRISEL) 5701-5702:
a quad/instance PRISEL 5701 for requesting and selecting between a
quad/instance 5711 from Bank 0 and a second quad/instance 5712 from
Bank 1, and an internal node PRISEL 5702 for requesting and
selecting between an internal node from Bank 0 5713 and an internal
node from Bank 1 5714.
[0576] In one embodiment, the quad/instance priority selection
logic 5701 prioritizes one of the first QI node 5711 and second QI
node 5712, storing the prioritized result in the ray tracing queue
(RTQ) for further processing (e.g., intersection testing).
Similarly, internal node PRISEL logic 5702 prioritizes one of the
internal BVH nodes 5713-5714 on which a ray tracing traversal (RTT)
box test is performed. In one embodiment, only one request is
selected from each bank (e.g., one of requests 5711 and 5712 and
one of requests 5713 and 5714). The launch of these requests may
also reset the stack data present (DP) bit, as indicated, so that
this entry is not retrieved in response to a node fetch operation.
In one embodiment, for the instance fetch operation, the ray's data
present (DP) bit is reset when the instance request is sent, and
finally set when the ray is transformed after the node fetch.
[0577] As part of this process, for every quad test dispatch where
the node type is non-opaque, the shader record identifier null
lookup is dispatched as a bindless thread dispatch (BTD) based on
the following shader record identifier lookup address: [0578]
sri_null_lookup_ptr[47:3]=2*(Ray.hitGroupSRBasePtr+Node.leafDesc.Shaderin-
dex*ray.SRStride)+1; [0579] sri_null_lookup_tag[7:0]={1'd0,
RTT_INST, rtt_alloc_entry[5:0]};
[0580] In one embodiment, a quad/instance (QI) decouple FIFO is
included to resolve temporal stack FIFO full conditions and to
implement synchronous updates to the hitinfo/ray with a push into
the stack FIFO (see, e.g., stack FIFO 6001 in FIG. 60). This is
done so that the ray/hitinfo has a guaranteed data present (DP) bit
set in subsequent processes. Note that ray/hitinfo may be assigned
a fixed high priority when colliding with memory writes.
[0581] The return from RTQ can result in an Instance (e.g., an
instance transformation) or a Quad (i.e., traversal/intersection
test results) on two separate interfaces. Below are the two return
FIFOs used for processing results in one embodiment: [0582] a.
Instance Return FIFO: Update rt_ray.rt_ray_data=rtq_rt_ray_data;
ray_dirty[Entry]=1; [0583] b. Quad Return FIFO: [0584] i. If the
Quad is non-opaque and
(T.sub.far<P.sub.rev_T.sub.far).fwdarw.Check SRI_NULL_DP to pop
(read from) the quad/instance (QI) decoupled FIFO. Note that in one
embodiment the Hitinfo write from the ray tracing queue (RTQ) FIFO
has higher priority over MemHitInfo. [0585] 1. If
(KSP_NULL=1).fwdarw.Treat the non-opaque quad as if it were opaque
and update T.sub.far. [0586] 2. If (KSP_NULL !=1).fwdarw. [0587]
Write the potential HitInfo to memory with the valid bit set to 1.
[0588] Read T, U, V, Leaf Type, PrimLeafIndex, and Front Face from
the RTQ [0589] Read PrimIndexDelta, PrimleafPtr from NodeData.
Update instanceLeafPtr from Ray Data. [0590] hitGroupRecPtr as
computed above [0591] ii. If the quad is non-opaque and (T.sub.far
<P.sub.rev_T.sub.far) 4 [0592] Update the Committed HitInfo with
Valid=1. [0593] Read T,U,V, Leaf Type, PrimLeafIndex, Front Face
from the RTQ. [0594] Read PrimIndexDelta, PrimleafPtr from
NodeData. [0595] Update instanceLeafPtr from rt_ray.rt_ray_ctrl
[0596] hitGroupRecPtr as computed for above
[0597] In one embodiment, the return from the ray tracing traversal
(RTT) box intersection test may push into the stack 0/1 (5203/5204)
FIFO 6001 for further processing.
[0598] FIGS. 58 and FIGS. 59A-B illustrate an example of BVH-ray
processing using a "short" stack (e.g., such as stacks 5203 or
5204, which include a limited number of local stack entries). A
short stack is used to conserve high speed storage in combination
with intelligent node management techniques to provide a highly
efficient sequence of traversal operations. In the illustrated
example, the short stack 5203 includes entries for six BVH nodes.
However, the underlying principles of the invention may be
implemented using short stacks of various sizes.
[0599] Operations 5949-5972 push and pop stack entries during BVH
traversal. In one embodiment, the operations 5949-5972 are
performed on the stack 5203 by stack processing circuitry 5120 (see
FIG. 51). A specific traversal sequence is shown starting with the
root BVH node N 5900 at BVH level 0.
[0600] At 5949 the stack 5203 is initialized with node N, which is
then popped from the stack and processed, resulting in hits H0-H2
comprising child nodes N0-N2 5901-5903 at Level 1 of the BVH (i.e.,
"hits" meaning that ray traverses the three child nodes N0-N2
5901-5903). The three child node hits 5901-5902 are sorted based on
hit distance and pushed on the stack 5203 (operation 5950) in the
sorted order. Thus, in this embodiment, whenever a new set of child
nodes are evaluated, they are sorted based on hit distance and
written into the stack 5203 in the sorted order (i.e., with the
closer child nodes at the top of the stack).
[0601] The first child node N0 5901 (i.e., the closest child node)
is popped from the stack 5203 and processed, resulting in three
more child node hits N00-N02 5911-5913 at Level 2 of the BVH (the
"level" is sometimes referred to as the "depth" of the BVH nodes),
which are sorted and pushed to the stack 5203 (operation 5951).
[0602] Child node N00 5911 is popped from the stack and processed,
resulting in a single hit comprising a single child node N000 5920
at Level 3 of the BVH (operation 5952). This node is popped and
processed, resulting in six hits N0000-N0005 5931-5936 at level 4,
which are sorted and pushed to the stack 5203 (operation 5953). To
make room within the short stack 5203, nodes N1, N2, N02, N01 are
removed as indicated (i.e., to limit the short stack to six
entries). The first sorted node N0000 5931 is popped and processed,
generating three hits N00000-N00002 5931-5933 at Level 5 of the BVH
(operation 5954). Note N0005 is removed to make room on the short
stack 5203 for the new nodes.
[0603] In one embodiment, each time a node is removed from the
short stack 5203, it is saved back to memory. It will then be
re-loaded to the short stack 5203 at a later time (e.g., when it is
time to process the node in accordance with the traversal
operation).
[0604] Processing continues on FIG. 59A where nodes N00001 and
N00002 are popped and processed (operations 5955-5956) at Level 5
of the BVH. Nodes N0001, N0002, N0003, and N0004 at Level 4 are
then popped and processed (operations 5957-5960), resulting in an
empty short stack 5203.
[0605] Thus, a pop operation results in retrieval of the root BVH
node, Node N in accordance with the restart trail (RST) (operation
5961). The three child hits N0, N1, N2, from Level 1 are again
sorted and pushed to the short stack (operation 5962). Node N0 is
then popped and processed, followed by Nodes N00, N000, and N0005
(operations 5963-5965). Node N01 is popped and processed (operation
5966), followed by Node N02, Node N2, and Node N1 (operations
5967-5970), again resulting in an empty short stack. Consequently,
the next Level 2 node, N11 is popped from the short stack and
processed, completing the traversal (i.e., because Node N11 did not
result in a hit).
[0606] As mentioned, one embodiment of a traversal tracker 5248
updates the tracking array 5249 which identifies the child
node/subtree in each level of the BVH hierarchy which is currently
being traversed. In one implementation, the length of the tracking
array 5249 is equal to the depth of the BVH (6 in the illustrated
example) and each entry in the tracking array 5249 includes an
index value identifying the child subtree currently being
traversed. In one specific implementation, for an N-wide BVH (i.e.,
where each internal node references N child nodes) each entry in
the tracking array 5249 includes a log 2(N) bit value to identify
the child nodes/subtrees. In one embodiment, child nodes/subtrees
assigned an index smaller than the current child index have been
fully traversed and will therefore will not be revisited in the
event of a restart. In one embodiment, when last intersected child
is being traversed, the child index is set to the maximum value to
indicate that there are no more entries on the stack.
[0607] The short traversal stack 5203 may store the top few entries
of the stack in a circular array. In one implementation, each stack
entry in the short traversal stack 5203 includes an offset to a
node, miscellaneous information such as the node type (internal,
primitive, instance etc.) as well as one bit that indicates if this
child is the last (farthest) intersected child node in a parent
node. However, these specific details are not required for
complying with the underlying principles of the invention.
[0608] FIG. 60 illustrates one embodiment of the stack processing
circuitry/logic 5120 for performing stack management and traversal
operations as described above. A stack FIFO 6001 is loaded with any
child BVH nodes 6000 which require processing. For example, when a
box test or quad test is completed by the traversal processing
circuitry 5210, the results are pushed into the stack FIFO 6001 and
used to update the stack 5203. This may include, for example,
updates to the hit info such as the set of child nodes 6000
associated with a particular hit.
[0609] Stack processing circuitry/logic 6003 reads entries from the
stack 5203 with data required for processing each entry including
an indication as to whether the BVH node is an internal node or a
leaf node and associated index data. If the node is a leaf
node/quad, then the data may include quad descriptors and indices
as well as shader index data. The stack processing circuitry/logic
6003 then performs the stack processing operations described herein
such as identifying new nodes associated with a hit and sorting the
nodes based on hit distance. Although illustrated as a separate
entity, the stack processing circuitry/logic 6003 may be integrated
within the traversal circuitry 5102.
[0610] As indicated, the stack processing circuitry/logic 6003
generates stack updates 6011 as it completes processing each BVH
node from the stack 5203. For example, after reading an entry from
the stack 5203, it may update the various control bits such as the
data present (DP) bit and valid (VLD) bit. FIG. 60 illustrates the
evict ready and data present bits 6010 being set. A corresponding
stack update 6011 may also be sent to the stack 5203 (e.g.,
allowing old entries to be removed to make room for new child
nodes).
[0611] Stack updates may be controlled via arbitration circuitry
6012 which selects between updating the stack 5203 with the current
processing updates 6011, filling the stack 5203 from memory with
one or more new BVH child nodes (Mem Fill), and performing an
initial allocation to the stack from memory (e.g., starting with
the root node and one or more child nodes).
[0612] In one embodiment, when a quad/instance/internal node is
processed on the stack, one or more of the following operations may
be performed: [0613] i. Eviction of the stack entry due to multiple
conditions such as moving down the instance for a new BVH,
processing a hit procedural, an any hit shader, etc. [0614] ii.
Deallocate the Ray entry if the stack is evicted due to a hit
procedural and/or any hit shader. [0615] iii. Deallocate the cache
entry if that stack is evicted due to hit procedural and/or any hit
shader. [0616] iv. Update the ray control (BVH only) if the ray
needs to be passed down via the instance leaf to the new BVH.
[0617] FIGS. 61A-B illustrate tables for configuring read/write
ports and setting control bits for all ray tracing traversal
structures. In particular, example sub-structures, vertical
structures, and read/write actions are shown for rays 6101, hits
6102, and stacks 6103. Note, however, that the underlying
principles of the invention are not limited to these specific data
structures/operations.
Apparatus and Method for High Quality Ray-Traced Level of Detail
Transitions
[0618] On graphics processing architectures, the "level-of-detail"
(LOD) can refer to the selection of mesh resolutions based on
variables such as distance from the camera. LOD techniques are used
to reduce memory consumption and improve graphics processing
functions such as geometric aliasing in games. For example, the
details of a high resolution mesh may not be required when the mesh
is far away from the current perspective of the user.
[0619] In rasterization-based implementations, smooth transitions
between LODs are enabled using "stochastic LOD" techniques such as
described in Lloyd et al, Implementing Stochastic Levels of Detail
with Microsoft DirectX Raytracing (Jun. 15, 2020). Without these
stochastic techniques, the transition between LODs can result in
distracting artifacts where objects suddenly change in appearance
when a new LOD is selected. Using stochastic LODs, a cross-dissolve
between LOD levels is performed through a random assignment of
pixels to one of the LODs involved in the transition (e.g., either
the higher resolution or lower resolution LOD).
[0620] The above solution uses a binary mask and a binary
comparison value to achieve eight transitional steps for stochastic
LOD transitions when fading from a first LOD ("LOD0") to a second
LOD ("LOD1"). In this implementation, an 8-bit ray mask and an
8-bit instance mask are logically ANDed to determine if an instance
needs to be traversed. These 8-bit masks and the associated
bit-wise logic operations result in limited LOD transition
capabilities. For example, when transitioning between LOD0 and LOD1
of an object, where LOD0 has a fractional value of 0.25 and LOD1
has a fractional value of 0.75 (based on camera distance), the mask
for the instance would be set to LOD0 to enable only 2 random bits
(0.25 of 8 bits). The instance mask for LOD1 would be set to the
binary complement of the mask of LOD0, with 6 bits enabled. For any
given ray, one random bit is selected in the ray-mask to achieve a
random selection of either LOD0 (with a probability of 0.25) and
LOD1 (with a probability of 0.75). However, because only one of
eight bits is selected, there are only 8 intermediate steps for
transitioning between LOD0 and LOD1.
[0621] As shown in FIG. 62, in one embodiment of the invention, an
LOD selector 6205 is provided with an N-bit comparison operation
mask 6220 which is treated as a binary value to determine a
comparison operation to be performed. The selected comparison
operation is used to compare against the reference to allow for
more transitional LOD steps. In one embodiment, the comparison
operation is selected from less-than-or-equal-to (less_equal) and
greater-than (greater), although the underlying principles of the
invention are not limited to these specific comparison operations.
In one implementation, 8-bits are used (N=8) where 7 of the bits
define an unsigned integer value in the range of [0 . . . 127],
enabling 128 transitional steps for LOD cross-fading and 1 bit
indicates the comparison operation (e.g., if set to 0, then a
less_equal operation is performed and if set to 1, the greater
operation is performed). In one embodiment, a ray comparison mask
6221 may also be provided to the LOD selector 6205 in the range [0
. . . 127] as an additional ray parameter.
[0622] The following code sequence highlights how ray traversal
reacts to this new comparison mask, in one embodiment:
TABLE-US-00014 if( ray.InstanceMask & instance.InstanceMask ) {
if( ( instance.ComparisonMode == less_equal &&
instance.ComparisonMask <= ray.ComparisonMask ) | | (
instance.ComparisonMode == greater &&
instance.ConnparisonMask > ray.ComparisonMask ) ) {
traverseInstance(Instance); } }
[0623] In the above code sequence, the first IF statement tests
whether the binary masks allow traversal into the current instance.
If so, the second IF statement then tests the comparison mode
setting in view of the values for the instance comparison mask
(e.g., comparison operation mask 6220) and ray comparison mask
6221.
[0624] Returning to the above LOD transition example, for the
instance of LOD0 with a fractional value of 0.25, the first 7 bits
are set to a value of 31 (=int(0.25*127)), and the last bit is set
to 0 (indicating the less_equal operation). For the instance of
LOD1 with a fractional value of 0.75, the first 7 bits are set to
value of 31 (=int((1.0-0.75)*127)), and the last bit is set to 1
(indicating the greater operation). Thus, for this implementation,
if a uniformly distributed random number is generated in the range
[0 . . . 127] as a ray comparison mask, there are up to 127
transitional steps which may be selected by LOD selector 6205 for
transitioning between LOD0 and LOD1.
[0625] While the specific details set forth above are used for the
purpose of explanation, the underlying principles of the invention
may be implemented with other details. For example, other
comparison operators may be used in place of, or in addition to
less_equal and greater. For example, comparison operators such as
not_equal, equal, less and greater_equal (greater than or equal to)
may also be used. One implementation includes a ray flag and an
instance flag that disables ANDed ray masks and enables the use of
these bits as comparison masks.
[0626] Embodiments of the invention include a combination of fixed
function acceleration circuitry and general purpose processing
circuitry to perform ray tracing. For example, certain operations
related to ray traversal of a bounding volume hierarchy (BVH) and
intersection testing may be performed by the fixed function
acceleration circuitry, while a plurality of execution circuits
execute various forms of ray tracing shaders (e.g., any hit
shaders, intersection shaders, miss shaders, etc). One embodiment
includes dual high-bandwidth storage banks comprising a plurality
of entries for storing rays and corresponding dual stacks for
storing BVH nodes. In this embodiment, the traversal circuitry
alternates between the dual ray banks and stacks to process a ray
on each clock cycle. In addition, one embodiment includes priority
selection circuitry/logic which distinguishes between internal
nodes, non-internal nodes, and primitives and uses this information
to intelligently prioritize processing of the BVH nodes and the
primitives bounded by the BVH nodes.
Acceleration Data Structure Compression
[0627] The construction of acceleration data structures is one of
the most important steps in efficient ray-traced rendering. In
recent times, the bounding volume hierarchy (BVH) acceleration
structure, described extensively herein, has become the most widely
used structure for this purpose. The BVH is a hierarchical tree
structure which serves to spatially index and organize geometry
such that ray/primitive intersection queries can be resolved very
efficiently. The ability to resolve these queries is one of the
most critical operations for ray-traced rendering. While the
embodiments of the invention described below operate on a BVH
structure, the underlying principles of the invention are not
limited to a BVH. These embodiments may be applied to any other
acceleration data structure with similar relevant features.
[0628] Producing a BVH is typically referred to as "constructing"
or "building" the BVH. Although a number of BVH construction
algorithms have been proposed, top-down BVH builders are
predominantly used for achieving high rendering efficiency for both
real-time and offline rendering applications. Top-down BVH build
algorithms typically maintain one or more temporary arrays during
construction. These arrays hold data necessary to sort/organize
geometry to produce the BVH structure. These arrays are read and/or
written multiple times during the build (typically 1-2 times per
level of the BVH hierarchy). As these arrays are often of
considerable size, this process is bandwidth-intensive. Thus,
improvements in BVH build compute performance, such as could be
expected from a hardware BVH builder, are likely to have only a
limited impact if this bandwidth issue is not addressed.
[0629] One embodiment of the invention includes a compression
scheme for the temporary data maintained by many top-down BVH
builders. The purpose of this compression scheme is to reduce the
bandwidth required for BVH construction, thereby enabling faster
and more efficient BVH construction. Note, however, that the
embodiments of the invention may be used for other kinds of BVH
builders and with other types of acceleration data structures, such
as kd-trees.
[0630] Many top-down BVH builders maintain two primary types of
data during the BVH build: (1) an axis aligned bounding box (AABB)
for each primitive involved in the BVH build; and (2) an unsigned
integer index associated with each primitive, which points to one
of these AABBs, and/or to the original primitive from which the
AABB was produced.
[0631] One embodiment of the invention utilizes a Structure of
Arrays (SOA) layout for combining each AABB with a single integer
index. The AABBs are maintained in one array, and the integer
indices in a second array. Only the index array must be reordered
to achieve BVH construction. Storing the build data in this fashion
leads to a number of advantages. In this layout scheme, the AABB
data is largely read-only, and AABB write bandwidth is not incurred
for most of the build process.
[0632] By using an SOA structure, only the AABBs need to be
infrequently compressed during the build. In fact, the AABB data
may only need to be compressed once before build as a pre-process,
depending on the implementation. Since the build is performed by
partitioning the index arrays, one embodiment of the invention
re-compresses these at every level of the build.
[0633] By operating on compressed versions of these arrays instead
of their conventional, uncompressed counterparts, the bandwidth
required for BVH construction is reduced. The compressed versions
of the arrays are stored temporarily, and used only for the purpose
of the build. They are discarded once build is complete, leaving a
BVH which references the original input list of primitives.
[0634] An important characteristic of the compression techniques
described herein is that they are cache line-aware. Both of the
compressed arrays are stored as an array of Compression Blocks of
fixed size, where the size is a whole number of cache lines. This
number is greater than or equal to one. The Compression Blocks of
each of the two types of array do not need to be the same size.
These two types of blocks are referred to herein as AABB
Compression Blocks and Index Compression Blocks.
[0635] Note that the underlying principles of the invention do not
require that the size of the blocks is a whole number of
cachelines. Rather, this is one of several optional features
described herein. In one embodiment described below, this
functionality is control by the variables
AABBCompressionBlockSizeBytes and IndexCompressionBlockSizeBytes in
Tables B and D, respectively.
[0636] Because the spatial extent of, and number of primitives
referenced by, each node will generally decrease as the top-down
build proceeds from the root to the leaves of the tree structure,
different representations of the AABBs may be appropriate at
different stages of construction. For example, the accuracy of the
compressed AABBs may be less critical at the upper levels of the
tree, whereas more precise representations may be needed at the
lower levels to maintain reasonable tree quality. It may therefore
be adequate to use lossy compression near the root of the tree to
maximize bandwidth savings, and switch to an uncompressed, lossless
representation of the primitives for the lower levels. This divides
BVH construction into at least two phases illustrated in FIG. 63: a
top phase 6301 for nodes at or above a specified level of the
hierarchy (Nodes 0, 1, 8) and a bottom phase 6302 for nodes below
the specified level (Nodes 2-7, 9-14). A multi-level build can
proceed in such a fashion that the entirety of an upper level
hierarchy (e.g. the `Top` portion in FIG. 63) is built before any
node in the lower levels are built, or the building of the levels
can be interleaved. If an upper level is built entirely before any
lower levels, nodes which must be split at a lower level of the
build can be stored on a structure such as a queue to be
partitioned at a later stage.
[0637] As an alternative to using a full-precision copy of the
AABBs for the lower levels 6302, another variation of the scheme is
to "re-compress" the AABBs during build for use in building the
lower levels. By doing so, geometry can be compressed relative to
the extent of individual subtrees. Since individual subtrees
generally represent a smaller spatial extent compared to the root
node, this can benefit the accuracy of the compressed
representation, or the efficiency of compression. A similar pattern
for a multi-level compressed build is observed in current research.
The divide 6300 between different phases of construction can be
defined according to a variety of node characteristics. One
embodiment uses a fixed number of primitives to act as a threshold
value.
[0638] A variation used in some embodiments of the invention
instead opt to employ a single-level build only. For example, a
single, compressed representation of the build data could be used
to build the entire tree.
I. AABB Compression
[0639] In one embodiment of the invention, the input to the AABB
compression logic (which may be implemented in hardware and/or
software) is an array of uncompressed primitives and the output is
an array of AABB compression blocks, which are of a fixed size, and
aligned to some number of cache lines. Since the effective AABB
compression ratio at any particular region of the mesh is highly
data-dependent, one embodiment packs a variable number of AABBs per
AABB compression block.
[0640] As shown in FIG. 64, one embodiment of the compression block
6400 is organized in two main parts: Meta Data 6401 and Vector
Residuals 6402. The MetaData 6401 provides per-block information
and constants required to decode the Vector Residuals 6402 into a
list of AABBs. The Vector Residuals 6402 store the bulk of the
compressed information used to represent the AABBs. Each of these
elements are described in more detail below.
[0641] Briefly, in one embodiment, delta compression is used. A
seedVector comprises a baseline set of AABB values and the vector
residuals 6402 provide offsets to these baseline values to
reconstruct each AABB. The numResiduals value specifies the number
of vector residuals 6402 and the residualSizeVector specifies the
size of the residuals 6402.
AABB Global Compression Constants
[0642] In addition to the per-block constants that are stored in
each compression block 6400, a set of AABB Global Compression
Constants may store information relating to all of the blocks in
the entire compression process. These are summarized in Table B for
one particular implementation.
TABLE-US-00015 TABLE B Constant Description NQ {X, Y, Z} Three
values which denote the number of bits used for quantization of
vertex components in each of the three spatial dimensions.
AABBCompression- Size in Bytes of an AABB Compression
BlockSizeBytes Block. This value will typically be aligned to a
certain number of cache lines. maxAABBsPerBlock The maximum number
of AABBs allowed in an AABB Compression Block. This constant is
used along with the numResidualVectorsPerPrimitive Global
Compression Constant to determine the number of bits needed for the
numResiduals value shown in FIG. 64. numResidualVectors- This value
keeps track of the number of PerPrimitive residual vectors being
used to represent an AABB in the compressed blocks. A regular AABB
normally consists of two 3D vectors, min and max. However, it is
possible that the representation of the AABB can be transformed to
a structure with a different number of vectors. An example of this
is discussed in the later section on Error! Reference source not
found., where a pair of 3D vectors are transformed to a single 6D
vector. It is necessary for the compression algorithm to keep track
of this value to perform a number of core operations correctly.
residualNum- This constant is used to keep track of Dimensions how
many dimensions the residual vectors will have at the point they
are added to the AABB Compression Blocks. This value is needed as
it is possible for the 3D AABB data to be transformed to a
different number of dimensions during compression.
AABB Compression Flow
[0643] One embodiment of the AABB compression process involves
iterating through the input array of primitives in turn, and
outputting an array of AABB Compression Blocks 6400. The output
array contains a minimal number of AABB Compression Blocks 6400
needed to represent the AABBs of the primitives in compressed
form.
[0644] FIG. 65 illustrates a process in accordance with one
particular embodiment. As mentioned, the compression process is not
limited to any particular architecture and may be implemented in
hardware, software, or any combination thereof.
[0645] At 6501 an array of primitives for a BVH build is provided.
At 6502, the next primitive in the array (e.g., the first primitive
at the start of the process) is selected and its AABB is evaluated
for compression. If the AABB fits within the current compression
block, determined at 6503 (e.g., based on its mix/max data), then
the AABB is added to the current compression block at 6504. As
mentioned, this can include determining residual values for the
AABB by calculating the distances to an existing base vector within
the compression block (e.g., the seedVector).
[0646] In one embodiment, if the AABB of the primitive does not fit
within the compression block, then the current compression block is
finalized at 6510 and stored in memory within the output array. At
6511, a new compression block is initialized using the AABB of the
primitive. In one embodiment, the primitive AABB is used as the
seed vector for the new compression block. Residuals may then be
generated for subsequent AABBs of primitive based on distances to
the new seed vector. In one implementation, the first residual,
generated for the second AABB, is determined based on distance
values to the seed vector values. The second residual, for the
third AABB, is then determined based on distances to the first
residual. Thus, a running difference is stored, as described in
greater detail below. Once the current primitive is compressed, the
process returns to 6502 where the next primitive in the array is
selected for compression.
[0647] Thus, visiting each primitive in turn, its AABB is
determined (e.g., as a float value). A series of operations are
then performed to the AABB to achieve compression and the
compressed result is added to the current AABB Compression Block in
the output array. If the compressed AABB fits, it is added to the
current block, and the process moves to the next AABB. If the AABB
does not fit, the current AABB Compression Block is finalized, and
a new AABB Compression block is initialized in the output array. In
this way, the number of compressed blocks needed to store the AABBs
is minimized.
[0648] The pseudocode below in TABLE C shows the flow of AABB
compression according to one particular embodiment of the
invention. Note, however, that the underlying principles of the
invention are not necessarily limited to these details.
[0649] As shown in the pseudocode sequence, for each AABB
Compression Block, an integer is written in a separate array
(blockOffsets) which records the position in the original primitive
array at which each AABB Compression Block starts (i.e., the first
primitive AABB it contains). The blockOffsets array is used during
the build for resolving the original primitive IDs that the
compressed block represents.
AABB Residual Computation
[0650] In one embodiment, each input AABB goes through a set of
stages to compress it before adding it to a compressed block,
resulting in the Vector Residuals shown in FIG. 64. The process is
captured as the code on line 26 of Table C, where the
CompressionCore is used to convert the AABB to a list of compressed
vectors.
TABLE-US-00016 TABLE C 1: uint numBoxesEncoded = 0; 2: uint
blockStartIndex = 0; 3: uint currentBlock = 0; 4:
CompressedAABBBlock compressedBlocks = [ ] 5: uint blockOffsets = [
] 6: uint totalNumBoxes = geometry.getNumPrimitives( ); 7: uint
maxBitsPerBlock = AABBCompressionBlockSizeBytes * 8; 8: uint
numBitsRequiredCurrentBlock = 0; 9: 10: while (numBoxesEncoded <
totalNumBoxes) 11: { 12: CompressionCore cCore; 13:
InitBlock(compressedBlocks, currentBlock); 14:
blockOffsets.append(numBoxesEncoded); 15: blockStartIndex =
numBoxesEncoded; 16: numBitsRequiredCurrentBlock = 0; 17: 18:
while(numBitsRequiredCurrentBlock < maxBitsPerBlock &&
19: numBoxesEncoded < totalNumBoxes && 20:
(numBoxesEncoded - blockStartIndex) < maxAABBsPerBlock) 21: {
22: Primitive p = geometry.getPrimitive(numEncoded); 23: AABB box =
p.getBoundingBox( ); 24: 25: Vector compressedVectors = [ ]; 26:
compressedVectors = cCore.compress(box); 27:
numBitsRequiredCurrentBlock = 28:
TestAddToBlock(compressedBlocks[currentBlock], compressedVectors);
29: 30: if(numBitsRequiredCurrentBlock <= maxBitsPerBlock) 31: {
32: CommitToBlock(compressedBlocks[currentBlock],
compressedVectors); 33: numBoxesEncoded++; 34: } 35: else 36:
break; 37: } 38: 39:
FinalizeBlock(compressedBlocks[currentBlock++]); 40: } 41: 42:
if(numBoxesEncoded - blockStartIndex > 0) 43:
FinalizeBlock(compressedBlocks[currentBlock++]);
[0651] In one embodiment, compression of an AABBs occurs in the
following stages: (1) quantization, (2) transform, and (3)
prediction/delta coding.
[0652] 1. Quantization
[0653] In one embodiment, the floating-point AABB values are first
quantized to an unsigned integer representation using a fixed
number of bits per axis. This quantization step may be performed in
a variety of ways. For example, in one implementation, the
following values for each axis i are determined:
L.sub.i=S.sub.max,i-S.sub.min,i
N.sub.B,i=2.sup.NQ.sub.i
VU.sub.min,i=(VF.sub.min,i-S.sub.min,i)/L.sub.i.times.N.sub.B,i
VU.sub.max,i=(VF.sub.max,i-S.sub.min,i)/L.sub.i.times.N.sub.B,i
where S.sub.min and S.sub.max are the minimum and maximum
coordinates of the entire set of geometry for which a BVH is to be
built, N.sub.B,i is the number of cells in the quantized grid in
the i-th axis, NQ.sub.i corresponds to the value in Table B,
VU.sub.min and VU.sub.max are the minimum and maximum coordinates
of the quantized AABB, VF.sub.min and VF.sub.max are the minimum
and maximum coordinates of the original floating-point AABB, and
the subscript i denotes a given axis (i.di-elect cons.{x,y,z}). As
any floating-point computation can introduce error, the
intermediate values should be rounded up or down to minimize the
values of VU.sub.min and maximize the values of VU.sub.max. The
values may also be converted to integer and clamped to the valid
range, to ensure a watertight AABB residing inside the AABB of the
entire set of geometry.
[0654] S.sub.min and S.sub.max could also represent the extent of a
subset of the geometry (e.g. a subtree within a larger BVH). This
could occur, for example, in a multi-level compressed build as per
FIG. 63.
[0655] 2. Transform
[0656] In one embodiment, a transform stage is implemented in which
data is transformed into a form that is more amenable to
compression. Although a variety of transforms may be used, one
embodiment of the invention employs a novel transform referred to
herein as Position-Extent Transform, which combines VU.sub.min and
VU.sub.max into a single 6 dimensional (6D) vector per primitive,
VT, as shown below:
E.sub.x=VU.sub.max,x-VU.sub.min,x E.sub.y=VU.sub.max,y-VU.sub.min,y
E.sub.z=VU.sub.max,z-VU.sub.min,z
V.sub.T=(VU.sub.min,x,VU.sub.min,y,VU.sub.min,z,E.sub.x,E.sub.x,E.sub.y,-
E.sub.z)
where VU.sub.min{x,y,z} and VU.sub.max{x,y,z} are the components of
VU.sub.min and VU.sub.max respectively. Essentially, this transform
allows the position and extent/size characteristics of the AABB to
be treated separately in the remaining compression stages. As
mentioned, other transforms may also be used.
[0657] 3. Prediction/Delta Coding
[0658] In one implementation, a conventional delta coding technique
is used to achieve good compression performance. In one embodiment,
the first vector in each compression block is designated as a
"seed" vector and stored verbatim in the AABB compression block
6400, as shown in FIG. 64. For subsequent vectors, a running
difference of the values is stored (i.e., residuals 6402). This
corresponds to a prediction scheme where the prediction for the
next input vector in the sequence is always the previous input
vector, and the residual value is the difference between the
current and previous input vectors. Residual values 6402 in this
embodiment are thus signed values, which requires an additional
sign bit. Various other prediction/delta coding may be used while
still complying with the underlying principles of the
invention.
[0659] One embodiment stores the residual values 6402 with the
minimum number of required bits, in order to maximize compression.
Based on the size of the residual values at the end of the residual
coding steps, a certain number of bits will be required for each of
the vector dimensions to accommodate the range of values
encountered in that dimension.
[0660] The number of bits required are stored in a Residual Size
Vector (RSV), as illustrated in the metadata 6401 in FIG. 64. The
RSV is fixed for a given compression block 6400, and so all values
in a given dimension of a particular block use the same number of
bits for their residuals 6402.
[0661] The value stored in each element of the RSV is simply the
minimum number of bits needed to store the entire range of residual
values in the dimension as a signed number. While compressing a
given AABB Compression Block (i.e. lines 18-37 of Table C), a
running maximum of the number of bits needed to accommodate all the
vectors seen so far is maintained. The RSV is determined for each
newly-added AABB (i.e. CommitToBlock, line 32 of Table C) and
stored in the compression blocks' metadata.
[0662] To test whether a new AABB will fit into the current block
(i.e. TestAddToBlock, line 28 of Table C and operation 6503 in FIG.
65), we compute the expected new RSV that would occur from adding
the new AABB, sum the expected RSV vector, and then multiply this
value by the total number of residuals that would exist in the
block if the new AABB was added. If this value is within the budget
available for storing residuals (i.e. less than or equal to the
total block size minus the meta data 6401 size), it can be added to
the current block. If not, then a new compression block is
initialized.
Entropy Coding
[0663] One embodiment of the invention includes an additional step
to the AABB residual computation which includes an entropy coding
of the residuals after prediction/delta coding. The underlying
principles of the invention are not limited to this particular
implementation.
Pre-Sorting/Re-Ordering Capability
[0664] As an optional pre-process, the input geometry can be
sorted/re-ordered to improve spatial coherence, which may improve
compression performance. Sorting can be performed in a variety of
ways. One way to achieve this is to use a Morton Code sort. Such a
sort is already used as major step in other BVH builders to promote
spatial coherence in the geometry before extracting a
hierarchy.
[0665] The compressed AABBs can be written in any desired order,
but if the AABBs are reordered/sorted, then it is necessary to
store an additional array of integers which records the sorted
ordering. The array consists of a single integer index per
primitive. The build can proceed with the primary index used to
reference the re-ordered list of primitives. When the original
primitive ID is needed (such as when the contents of a leaf node
are being written), we must use the primary index to look up the
original primitive ID in the additional array to ensure that the
tree references the original input geometry list correctly.
II. AABB Decompression
[0666] In one embodiment, decompression of the AABBs is performed
for an entire AABB Compression Block 6400 at a time. The residual
data is first reconstructed by inspecting the metadata 6401 of the
compression block 6400 and interpreting the stored residuals based
on this information (e.g., adding the distance values to the seed
vector and prior residual values in the sequence). The inverse of
each of the AABB Compression Stages is then performed to decompress
the single-precision floating point AABBs represented by the
compression block.
[0667] One embodiment implements a variation of the decompression
step in the case of BVH builders which employ reduced-precision
construction techniques which are aligned to a compressed hierarchy
output. Such reduced-precision builders are described in the
co-pending application entitled "An Architecture for Reduced
Precision Bounding Volume Hierarchy Construction", Ser. No.
16/746,636, Filed Jan. 17, 2020, which is assigned to the assignee
of the present application. A reduced-precision builder performs
much of its computation in a reduced-precision, integer space.
Consequently, one embodiment of the invention aligns the
quantization step of the AABB Residual Computation described herein
with the quantization employed in the reduced-precision builder.
The AABBs may then be decompressed to integer only, aligned with
the coordinate space of whatever node is currently being processed
by the reduced-precision builder. A similar variation may be
implemented with a builder which does not output a compressed
hierarchy, but performs quantization of vertices.
III. Index Compression
[0668] In one embodiment of the invention, the index array is
compressed into an array of Index Compression Blocks. FIG. 66
illustrates one embodiment of an index compression block 6610
comprising metadata 6603 and index residuals 6602. The index array
differs from the AABB array as it must be re-compressed as the
indices are partitioned/reordered during the build process.
[0669] In many conventional BVH builders, indices are represented
as unsigned integers, generally with one index per primitive. The
purpose of the index array is to point to primitive AABBs. Each
AABB/primitive may be allocated a fixed size in memory. It is
therefore possible to randomly access any particular primitive p or
AABB a in the arrays. However, when AABB compression leads to a
variable number of AABBs per cache line, the AABB compression block
storing a given primitive is not easily determined after
compression. Storing conventional indices is therefore not
compatible with the AABB Compression Blocks described herein.
[0670] In one embodiment of the invention, the indexing techniques
used to identify the location of primitive AABBs also allow for
compression of the indices themselves. Two novel techniques are
referred to below as Block Offset Indexing (BOI) and Hierarchical
Bit-Vector Indexing (HBI). These indexing implementations may be
used alone or in combination in the various embodiments of the
invention. In addition, both indexing techniques can be used as
part of a multi-level build, as per FIG. 63, and both types of
indices may also be used as part of the same BVH build. These
indexing techniques allow the BVH build to proceed in a similar
manner to a conventional BVH builder, but with compressed
representations of both the AABB and the corresponding index
arrays.
Global Index Compression Constants
[0671] Index compression employs a set of Global Index Compression
Constants, which apply to all Index Compression Blocks. Both of the
index compression schemes described below share the same global
constants, which are summarized in Table D below.
TABLE-US-00017 TABLE D Constant Description IndexCompression- Size
in Bytes of an Index BlockSizeBytes Compression Block. This value
will typically be aligned to a certain number of cache lines.
maxIndicesPerBlock The maximum number of indices allowed in an
Index Compression Block. This value determines the number of bits
needed to store the number of indices represented by a given
block.
Block Offset Indexing
[0672] In Block Offset Indexing (BOI), the regular single-integer
index is changed to a structure containing two integers, one of
which identifies the compression block 6400 and one of which
comprises an offset to identify the primitive AABB data within the
compression block 6400. One embodiment of the new data structure is
generated in accordance with the following code sequence:
TABLE-US-00018 struct blockOffsetIndex { uint blockIdx; uint
blockOffset; }
Here, blockIdx stores an index to an AABB Compression Block, and
blockOffset references a specific primitive AABB inside the block
(i.e., blockIdx in combination with blockOffset provides the
address of the primitive AABB). This information is sufficient to
fully reference a particular AABB within its compression block
during a build.
[0673] In one embodiment, one of these structures is generated for
each primitive in the BVH build, so the size of the list is
predictable. However, given a variable number of AABBs per AABB
Compression Block, there will be a variable number of these index
structures for each of these compression blocks (e.g., not all
possible values of blockOffset will exist for each AABB Compression
Block). Therefore, to correctly initialize the array of Block
Offset Indices, it is necessary to refer to the blockOffsets array
(see, e.g., the code sequence in Table C), from which the number of
primitives in each AABB Compression Block can be determined, either
concurrently with, or as a post-process to, the AABB compression.
Once initialized, the Block Offset Indices can be treated in
essentially the same manner as conventional indices found in
conventional BVH builders.
[0674] Single-integer indices used in conventional BVH builders are
typically 4 bytes in size. In one embodiment, 26 bits are used for
blockIdx and 6 bits are used for blockOffset. In an alternate
embodiment, smaller numbers of bits are used for each variable to
reduce the overall memory footprint. In one embodiment, since a
fixed size for the blockOffset must be chosen, this places limits
on the maximum number of primitives per AABB Compression Block. In
the case of 6 bits, a maximum of 64 primitives can be represented
per AABB Compression Block.
[0675] The remaining item to address for Block Offset Indexing is
how compression can be achieved. Block Offset Indices are delta
coded and packed in order into Index Compression Blocks. Each block
is packed with as many indices as possible, and a new Index
Compression Block is started each time the previous one reaches
capacity. This is performed in a very similar manner to the AABB
Compression Blocks (as shown in Table C), leading to a variable
number of indices per Index Compression Block.
[0676] FIG. 66 illustrates one example of a block offset index
compression block 6610 comprising metadata 6603 identifying the
number of indices in addition to a residual size vector and seed
vector. In one embodiment, a two-channel encoding is used for the
index residuals 6602, where the blockIdx and blockOffset values are
separately delta-compressed. Similar to AABB Compression Blocks,
the index compression block 6610 stores an indication of the number
of indices in the block, the number of bits for the residuals (as
the residual size vector), and a seed vector comprising a first
seed vector for blockIdx and a second seed vector for blockOffset.
The index residual values 6602 comprise a pair of difference values
resulting from compression. For example, an index residual value
may comprise a first difference value representing a difference
between the current input blockIdx value and a prior input blockIdx
value and a second difference value representing a difference
between the current input blockOffset value and a prior input
blockOffset value. The first blockIdx and blockOffset values in the
sequence are stored verbatim in the seedVector field, which
represents the vector from which the first residual value is
computed.
Hierarchical Bit-Vector Indexing
[0677] One embodiment of the invention uses another primitive index
compression technique referred to as Hierarchical Bit-Vector
Indexing (HBI), which may be used alone or in combination with
Block Offset Indexing (BOI). HBI is unlike both conventional
integer indices and BOI in that a single HBI Index can reference
multiple primitives at once. In fact, an HBI Index can reference up
to an entire AABB Compression Block.
[0678] An expanded structure of this type of index is shown in
FIGS. 67A-B. Each HBI index 6700 consists of two elements. The
blockIdx 6708 points to a given AABB Compression Block, serving the
same purpose as the corresponding element in Block Offset Indices.
The second component is a bit vector 6701 which has a number of
bits equal to the maximum number of AABBs allowed in an AABB
Compression Block (i.e., maxAABBsPerBlock). Each bit in the bit
vector 6701 signifies if the corresponding element in the AABB
Compression Block is referenced by this index. For example, if the
third bit in the bit-vector is a `1`, this signifies that the third
AABB/primitive of the AABB Compression Block is referenced by the
HBI index. If the bit is `0`, then that AABB/primitive is not
referenced.
Apparatus and Method for Displaced Mesh Compression
[0679] One embodiment of the invention performs path tracing to
render photorealistic images, using ray tracing for visibility
queries. In this implementation, rays are cast from a virtual
camera and traced through a simulated scene. Random sampling is
then performed to incrementally compute a final image. The random
sampling in path tracing causes noise to appear in the rendered
image which may be removed by allowing more samples to be
generated. The samples in this implementation may be color values
resulting from a single ray.
[0680] In one embodiment, the ray tracing operations used for
visibility queries rely on bounding volume hierarchies (BVHs) (or
other 3D hierarchical arrangement) generated over the scene
primitives (e.g., triangles, quads, etc) in a preprocessing phase.
Using a BVH, the renderer can quickly determine the closest
intersection point between a ray and a primitive.
[0681] When accelerating these ray queries in hardware (e.g., such
as with the traversal/intersection circuitry described herein)
memory bandwidth problems may arise due to the amount of fetched
triangle data. Fortunately, much of the complexity in modeled
scenes is produced by displacement mapping, in which a smooth base
surface representation, such as a subdivision surface, is finely
tessellated using subdivision rules to generate a tessellated mesh
6991 as shown in FIG. 69A. A displacement function 6992 is applied
to each vertex of the finely tessellated mesh which typically
either displaces just along the geometric normal of the base
surface or into an arbitrary direction to generate a displacement
mesh 6993. The amount of displacement that is added to the surface
is limited in range.
[0682] One embodiment of the invention effectively compresses
displacement-mapped meshes using a lossy watertight compression. In
particular, this implementation quantizes the displacement relative
to a coarse base mesh, which may match the base subdivision mesh.
In one embodiment, the original quads of the base subdivision mesh
may be subdivided using bilinear interpolation into a grid of the
same accuracy as the displacement mapping.
[0683] FIG. 69B illustrates compression circuitry/logic 6900 that
compresses a displacement mapped mesh 6902 in accordance with the
embodiments described herein to generate a compressed displaced
mesh 6910. In the illustrated embodiment, displacement mapping
circuitry/logic 6911 generates the displacement-mapped mesh 6902
from a base subdivision surface. FIG. 70A illustrates an example in
which a primitive surface 7000 is finely tessellated to generate
the base subdivision surface 7001. A displacement function is
applied to the vertices of the base subdivision surface 7001 to
create a displacement mapping 7002.
[0684] Returning to FIG. 69B, in one embodiment, a quantizer 6912
quantizes the displacement-mapped mesh 6902 relative to a coarse
base mesh 6903 to generate a compressed displaced mesh 6910
comprising a 3D displacement array 6904 and base coordinates 6905
associated with the coarse base mesh 6903. By way of example, and
not limitation, FIG. 70B illustrates a set of difference vectors
d1-d4 7022, each associated with a different displaced vertex
v1-v4.
[0685] In one embodiment, the coarse base mesh 7003 is the base
subdivision mesh 6301. Alternatively, an interpolator 6921
subdivides the original quads of the base subdivision mesh using
bilinear interpolation into a grid of the same accuracy as the
displacement mapping.
[0686] The quantizer 6912 determines the difference vectors d1-d4
7022 from each coarse base vertex to a corresponding displaced
vertex v1-v4 and combines the difference vectors 7022 in the 3D
displacement array 6904. In this manner, the displaced grid is
defined using just the coordinates of the quad (base coordinates
6905), and the array of 3D displacement vectors 6904. Note that
these 3D displacement vectors 6904 do not necessarily match to the
displacement vectors used to calculate the original displacement
7002, as a modelling tool would normally not subdivide the quad
using bilinear interpolation and apply more complex subdivision
rules to create smooth surfaces to displace.
[0687] As illustrated in FIG. 70C, grids of two neighboring quads
7090-7091 will seamlessly stitch together, as along the border
7092, both quads 7090-7091 will evaluate to the exact same vertex
locations v5-v8. As the displacements stored along the edge 7092
for neighboring quads 7090-7091 are also identical, the displaced
surface will not have any cracks. This property is significant, as
this, in particular means that the accuracy of the stored
displacements can be reduced arbitrarily for an entire mesh,
resulting in a connected displaced mesh of lower quality.
[0688] In one embodiment, half-precision floating point values are
used to encode the displacements (e.g., 16-bit floating point
values). Alternatively, or in addition, a shared exponent
representation is used that stores just one exponent for all three
vertex components and three mantissas. Further, as the extent of
the displacement is normally quite well bounded, the displacements
of one mesh can be encoded using fixed point coordinates scaled by
a constant to obtain sufficient range to encode all displacements.
One embodiment of the invention uses bilinear patches as base
primitives, using flat triangles, while another embodiment uses
triangle pairs to handle each quad.
[0689] A method in accordance with one embodiment of the invention
is illustrated in FIG. 71. The method may be implemented on the
architectures described herein, but is not limited to any
particular processor or system architecture.
[0690] At 7101 a displacement-mapped mesh is generated from a base
subdivision surface. For example, a primitive surface may be finely
tessellated to generate the base subdivision surface. At 7102, a
base mesh is generated or identified (e.g., such as the base
subdivision mesh in one embodiment).
[0691] At 7103, a displacement function is applied to the vertices
of the base subdivision surface to create a 3D displacement array
of difference vectors. At 7104, the base coordinates associated
with the base mesh are generated. As mentioned, the base
coordinates may be used in combination with the difference vectors
to reconstruct the displaced grid. At 7105 the compressed displaced
mesh is stored including the 3D displacement array and the base
coordinates.
[0692] The next time the primitive is read from storage or memory,
determined at 6506, the displaced grid is generated from the
compressed displaced mesh at 7103. For example, the 3D displacement
array may be applied to the base coordinates to reconstruct the
displaced mesh.
Enhanced Lossy Displaced Mesh Compression and Hardware BVH
Traversal/Intersection for Lossy Grid Primitives
[0693] Complex dynamic scenes are challenging for real-time ray
tracing implementations. Procedural surfaces, skinning animations,
etc., require updates of triangulation and accelerating structures
in each frame, even before the first ray is launched.
[0694] Instead of just using a bilinear patch as base primitive,
one embodiment of the invention extends the approach to support
bicubic quad or triangle patches, which need to be evaluated in a
watertight manner at the patch borders. In one implementation, a
bitfield is added to the lossy grid primitive indicating whether an
implicit triangle is valid or not. One embodiment also includes a
modified hardware block that extends the existing tessellator to
directly produce lossy displaced meshes (e.g., as described above
with respect to FIGS. 69A-71), which are then stored out to
memory.
[0695] In one implementation, a hardware extension to the BVH
traversal unit takes a lossy grid primitive as input and
dynamically extracts bounding boxes for subsets of
implicitly-referenced triangles/quads. The extracted bounding boxes
are in a format that is compatible with the BVH traversal unit's
ray-box testing circuitry (e.g., the ray/box traversal unit 8930
described below). The result of the ray vs. dynamically generated
bounding box intersection tests are passed to the ray-quad/triangle
intersection unit 8940 which extracts the relevant triangles
contained in the bounding box and intersects those. In one
embodiment, the "relevant" triangles are those triangles bounded by
the bounding box.
[0696] One implementation also includes an extension to the lossy
grid primitive using indirectly referenced vertex data (similar to
other embodiments), thereby reducing memory consumption by sharing
vertex data across neighboring grid primitives. In one embodiment,
a modified version of the hardware BVH triangle intersector block
is made aware of the input being triangles from a lossy displaced
mesh, allowing it to reuse edge computation for neighboring
triangles. An extension is also added to the lossy displaced mesh
compression to handle motion blurred geometry.
[0697] As described above, assuming the input is a grid mesh of
arbitrary dimensions, this input grid mesh is first subdivided into
smaller subgrids with a fixed resolution, such as 4.times.4
vertices as illustrated in FIG. 72.
[0698] As shown in FIG. 73, in one embodiment a lossy 4.times.4
grid primitive structure (GridPrim) is now computed based on the
4.times.4 input vertices. One implementation operates in accordance
with the following code sequence:
TABLE-US-00019 struct GridPrim { PrimLeafDesc leafDesc; // 4B
uint32_t primIndex; // 4B float3 vertex[4]; // 48B struct { exp :
7; // shared exponent disp_x : 5; disp_y : 5; disp_z : 5; }
disp_mag [16]; // 44B }; // 64 bytes total
[0699] In one implementation, these operations consume 100 bytes:
18 bits from PrimLeafDesc can be reserved to disable individual
triangles, e.g., a bit mask of (in top-down, left-right order)
000000000100000000b would disable the highlighted triangle 7401
shown in FIG. 74.
[0700] Implicit triangles may be either 3.times.3 quads (4.times.4
vertices) or more triangles. Many of these implicit triangles and
quads are stitched together to form a mesh. The mask tells us
whether we want to intersect the triangle. If a hole is reached,
deactivate the individual triangles per the 4.times.4 grid. This
enables greater precision and significantly reduced memory usage:
.about.5.5 bytes/triangle, which is a very compact representation.
In comparison, if a linear array is stored in full precision, each
triangle takes 48 and 64 bytes.
[0701] As illustrated in FIG. 75, a hardware tesselator 7550
tessellates patches to triangles in 4.times.4 units and stores them
into memory so BVHs can be built over them and they can be
ray-traced. In this embodiment, the hardware tessellator 7550 is
modified to directly support lossy displaced grid primitives.
Instead of generating individual triangles and passing them to the
rasterization unit, the hardware tessellation unit 7550 can
directly generate lossy grid primitives and store them to a cache
(e.g., an L0/L1 cache, a dedicated ray tracing cache, a shared
cache, etc), local memory (e.g., a local scratchpad memory), and/or
system memory.
[0702] An extension to the hardware BVH traversal unit 7550 that
takes a lossy grid primitive as input and on the fly extracts
bounding boxes for subsets of implicitly referenced
triangles/quads. In the example shown in FIG. 76, nine bounding
boxes 7601A to 7601-I, one for each quad, are extracted from the
lossy grid and passed as a special nine-wide BVH node to the
hardware BVH traversal unit 7550 to perform ray-box
intersection.
[0703] Testing all 18 triangles, one after the other, is very
expensive. Referring to FIG. 77, one embodiment extracts one
bounding box 7601A to 76011 for each quad. The nine bounding boxes
7601A to 76011 shown in FIG. 77 correspond to the nine quads 7601A
to 76011 shown in FIG. 76, although this is just an example; any
number of triangles could be extracted. When a subset of triangles
are read and bounding boxes computed, an N-wide BVH node 7700 is
generated--one child node 7601A-I for each quad. This structure is
then passed to the hardware traversal unit 7710 which traverses
rays through the newly constructed BVH. Thus, in this embodiment,
the grid primitive is used as an implicit BVH node from which the
bounding boxes can be determined. When a bounding box is generated,
it is known to contain two triangles. When the hardware traversal
unit 7710 determines that a ray traverses one of the bounding boxes
7601A-I, the same structure is passed to the ray-triangle
intersector 7715 to determine which object/triangle within the
bounding box has been hit. To determine if a bounding box has been
hit, the ray data comprising a ray origin and ray direction is
evaluated in view of the minimum and maximum coordinate values of
each bounding box 7601A-I. If a bounding box has been hit by the
ray, the ray-triangle intersector 7715 performs intersection tests
by evaluating the ray data in view of the triangle coordinates for
triangles contained in the bounding box.
[0704] In one embodiment of the invention, these techniques are
used as a pre-culling step to the ray-triangle traversal 7710 and
intersection units 7715. The intersection test is significantly
cheaper when the triangles can be inferred using only the BVH node
processing unit. For each intersected bounding box 7601A-I, the two
respective triangles are passed to ray-tracing triangle/quad
intersection unit 7715 to perform the ray-triangle intersection
tests.
[0705] The grid primitive and implicit BVH node processing
techniques described above may be integrated within or used as a
pre-processing step to any of the traversal/intersection units
described herein (e.g., such as ray/box traversal unit 8930
described below).
[0706] In one embodiment, extensions of such a 4.times.4 lossy grid
primitive are used to support motion-blur processing with two time
steps. One example is provided in the following code sequence:
TABLE-US-00020 struct GridPrimMB { PrimLeafDesc leafDesc; // 4B
uint32_t primIndex; // 4B float3 vertex_time0[4]; // 48B float3
vertex_time1[4]; // 48B // total 32 bytes up to here struct { exp :
6; // shared exponent disp_x : 6; disp_y : 6; disp_z : 6;
}disp_mag_time0[16],disp_mag_time1[16]; // 2x48B }; // 8 + 96 + 96
bytes total
[0707] Motion blur operations are analogous to simulating shutter
time in a camera. In order to ray-trace this effect, moving from t0
to t1, there are two representations of a triangle, one for t0 and
one for t1. In one embodiment, an interpolation is performed
between them (e.g., interpolate the primitive representations at
each of the two time points linearly at 0.5).
[0708] The downside of acceleration structures such as bounding
volume hierarchies (BVHs) and k-d trees is that they require both
time and memory to be built and stored. One way to reduce this
overhead is to employ some sort of compression and/or quantization
of the acceleration data structure, which works particularly well
for BVHs, which naturally lend to conservative, incremental
encoding. On the upside, this can significantly reduce the size of
the acceleration structure often halving the size of BVH nodes. On
the downside, compressing the BVH nodes also incurs overhead, which
may fall into different categories. First, there is the obvious
cost of decompressing each BVH node during traversal; second, in
particular for hierarchical encoding schemes the need to track
parent information slightly complicates the stack operations; and
third, conservatively quantizing the bounds means that the bounding
boxes are somewhat less tight than uncompressed ones, triggering a
measurable increase in the number of nodes and primitives that have
to be traversed and intersected, respectively.
[0709] Local quantization may be performed to reduce the size of
the BVH. An n-wide BVH node contains the axis-aligned bounding
boxes (AABBs) of its "n" children in single precision floating
point format. Local quantization expresses the "n" children AABBs
relative to the AABB of the parent and stores these value in
quantized e.g. 8 bit format, thereby reducing the size of BVH
node.
[0710] Local quantization of the entire BVH introduces multiple
overhead factors as (a) the de-quantized AABBs are coarser than the
original single precision floating point AABBs, thereby introducing
additional traversal and intersection steps for each ray and (b)
the de-quantization operation itself is costly which adds and
overhead to each ray traversal step. Because of these
disadvantages, compressed BVHs are only used in specific
application scenarios and not widely adopted.
[0711] One embodiment of the invention employs techniques to
compress leaf nodes for hair primitives in a bounding-volume
hierarchy as described in co-pending application entitled
"Apparatus and Method for Compressing Leaf Nodes of Bounding Volume
Hierarchies", Ser. No. 16/236,185, Filed Dec. 28, 2018, which is
assigned to the assignee of the present application. In particular,
as described in the co-pending application, several groups of
oriented primitives are stored together with a parent bounding box,
eliminating child pointer storage in the leaf node. An oriented
bounding box is then stored for each primitive using 16-bit
coordinates that are quantized with respect to a corner of the
parent box. Finally, a quantized normal is stored for each
primitive group to indicate the orientation. This approach may lead
to a significant reduction in the bandwidth and memory footprint
for BVH hair primitives.
[0712] In some embodiments, BVH nodes are compressed (e.g. for an
8-wide BVH) by storing the parent bounding box and encoding N child
bounding boxes (e.g., 8 children) relative to that parent bounding
box using less precision. A disadvantage of applying this idea to
each node of a BVH is that at every node some decompression
overhead is introduced when traversing rays through this structure,
which may reduce performance.
[0713] To address this issue, one embodiment of the invention uses
compressed nodes only at the lowest level of the BVH. Consequently,
the higher BVH levels, which are uncompressed, can be utilized at
optimal performance (i.e., they are touched often because they are
large, but there are very few of them), and compression on the
lower/lowest levels is also very effective, as most data of the BVH
is in the lowest level(s).
[0714] In addition, in one embodiment, quantization is also applied
for BVH nodes that store oriented bounding boxes. As discussed
below, the operations are somewhat more complicated than for
axis-aligned bounding boxes. In one implementation, the use of
compressed BVH nodes with oriented bounding boxes is combined with
using the compressed nodes only at the lowest level (or lower
levels) of the BVH.
[0715] Thus, one embodiment improves upon fully-compressed BVHs by
introducing a single, dedicated layer of compressed leaf nodes,
while using regular, uncompressed BVH nodes for interior nodes. One
motivation behind this approach is that almost all of the savings
of compression comes from the lowest levels of a BVH (which in
particular for 4-wide and 8-wide BVHs make up for the vast majority
of all nodes), while most of the overhead comes from interior
nodes. Consequently, introducing a single layer of dedicated
"compressed leaf nodes" gives almost the same (and in some cases,
even better) compression gains as a fully-compressed BVH, while
maintaining nearly the same traversal performance as an
uncompressed one.
[0716] FIG. 80 illustrates an exemplary ray tracing engine 8000
which performs the leaf node compression and decompression
operations described herein. In one embodiment, the ray tracing
engine 8000 comprises circuitry of one or more of the ray tracing
cores described above. Alternatively, the ray tracing engine 8000
may be implemented on the cores of the CPU or on other types of
graphics cores (e.g., Gfx cores, tensor cores, etc).
[0717] In one embodiment, a ray generator 8002 generates rays which
a traversal/intersection unit 8003 traces through a scene
comprising a plurality of input primitives 8006. For example, an
app such as a virtual reality game may generate streams of commands
from which the input primitives 8006 are generated. The
traversal/intersection unit 8003 traverses the rays through a BVH
8005 generated by a BVH builder 8007 and identifies hit points
where the rays intersect one or more of the primitives 8006.
Although illustrated as a single unit, the traversal/intersection
unit 8003 may comprise a traversal unit coupled to a distinct
intersection unit. These units may be implemented in circuitry,
software/commands executed by the GPU or CPU, or any combination
thereof.
[0718] In one embodiment, BVH processing circuitry/logic 8004
includes a BVH builder 8007 which generates the BVH 8005 as
described herein, based on the spatial relationships between
primitives 8006 in the scene. In addition, the BVH processing
circuitry/logic 8004 includes BVH compressor 8009 and a BVH
decompressor 8009 for compressing and decompressing the leaf nodes,
respectively, as described herein. The following description will
focus on 8-wide BVHs (BVH8) for the purpose of illustration.
[0719] As illustrated in FIG. 81, one embodiment of a single 8-wide
BVH node 8100A contains 8 bounding boxes 8101-8108 and 8 (64 bit)
child pointers/references 8110 pointing to the bounding boxes/leaf
data 8101-8108. In one embodiment, BVH compressor 8025 performs an
encoding in which the 8 child bounding boxes 8101A-8108A are
expressed relative to the parent bounding box 8100A, and quantized
to 8-bit uniform values, shown as bounding box leaf data
8101B-8108B. The quantized 8-wide BVH, QBVH8 node 8100B, is encoded
by BVH compression 8125 using a start and extent value, stored as
two 3-dimensional single precision vectors (2.times.12 bytes). The
eight quantized child bounding boxes 8101B-8108B are stored as 2
times 8 bytes for the bounding boxes' lower and upper bounds per
dimension. Note this layout differs from existing implementations
as the extent is stored in full precision, which in general
provides tighter bounds but requires more space.
[0720] In one embodiment, BVH decompressor 8026 decompresses the
QBVH8 node 8100B as follows. The decompressed lower bounds in
dimension i can be computed by
QBVH8.start.sub.i+(byte-to-float)QBVH8.lower.sub.i*QBVH8.extend.sub.i,
which on the CPU 4099 requires five instructions per dimension and
box: 2 loads (start,extend), byte-to-int load+upconversion,
int-to-float conversion, and one multiply-add. In one embodiment,
the decompression is done for all 8 quantized child bounding boxes
8101B-8108B in parallel using SIMD instructions, which adds an
overhead of around 10 instructions to the ray-node intersection
test, making it at least more than twice as expensive than in the
standard uncompressed node case. In one embodiment, these
instructions are executed on the cores of the CPU 4099.
Alternatively, a comparable set of instructions are executed by the
ray tracing cores 4050.
[0721] Without pointers, a QBVH8 node requires 72 bytes while an
uncompressed BVH8 node requires 192 bytes, which results in
reduction factor of 2.66.times.. With 8 (64 bit) pointers the
reduction factor reduces to 1.88.times., which makes it necessary
to address the storage costs for handling leaf pointers.
[0722] In one embodiment, when compressing only the leaf layer of
the BVH8 nodes into QBVH8 nodes, all children pointers of the 8
children 8101-8108 will only refer to leaf primitive data. In one
implementation, this fact is exploited by storing all referenced
primitive data directly after the QBVH8 node 8100B itself, as
illustrated in FIG. 81. This allows for reducing the QBVH8's full
64 bit child pointers 8110 to just 8-bit offsets 8122. In one
embodiment, if the primitive data is a fixed sized, the offsets
8122 are skipped completely as they can be directly computed from
the index of the intersected bounding box and the pointer to the
QBVH8 node 8100B itself.
[0723] When using a top-down BVH8 builder, compressing just the
BVH8 leaf-level requires only slight modifications to the build
process. In one embodiment these build modifications are
implemented in the BVH builder 8007. During the recursive build
phase the BVH builder 8007 tracks whether the current number of
primitives is below a certain threshold. In one implementation
N.times.M is the threshold where N refers to the width of the BVH,
and M is the number of primitives within a BVH leaf. For a BVH8
node and, for example, four triangles per leaf, the threshold is
32. Hence for all sub-trees with less than 32 primitives, the BVH
processing circuitry/logic 8004 will enter a special code path,
where it will continue the surface area heuristic (SAH)-based
splitting process but creates a single QBVH8 node 8100B. When the
QBVH8 node 8100B is finally created, the BVH compressor 8009 then
gathers all referenced primitive data and copies it right behind
the QBVH8 node.
[0724] The actual BVH8 traversal performed by the ray tracing core
8150 or CPU 8199 is only slightly affected by the leaf-level
compression. Essentially the leaf-level QBVH8 node 8100B is treated
as an extended leaf type (e.g., it is marked as a leaf). This means
the regular BVH8 top-down traversal continues until a QBVH node
8100B is reached. At this point, a single ray-QBVH node
intersection is executed and for all of its intersected children
8101B-8108B, the respective leaf pointer is reconstructed and
regular ray-primitive intersections are executed.
[0725] One embodiment of the leaf-level compression scheme allows
even for lossless compression of the actual primitive leaf data by
extracting common features. For example, triangles within a
compressed-leaf BVH (CLBVH) node are very likely to share
vertices/vertex indices and properties like the same objectID. By
storing these shared properties only once per CLBVH node and using
small local byte-sized indices in the primitives the memory
consumption is reduced further.
[0726] In one embodiment, the techniques for leveraging common
spatially-coherent geometric features within a BVH leaf are used
for other more complex primitive types as well. Primitives such as
hair segments are likely to share a common direction per-BVH leaf.
In one embodiment, the BVH compressor 8009 implements a
compression-scheme which takes this common direction property into
account to efficiently compress oriented bounding boxes (OBBs)
which have been shown to be useful for bounding long diagonal
primitive types.
[0727] The leaf-level compressed BVHs described herein introduce
BVH node quantization only at the lowest BVH level and therefore
allow for additional memory reduction optimizations while
preserving the traversal performance of an uncompressed BVH. As
only BVH nodes at the lowest level are quantized, all of its
children point to leaf data 8101B-8108B which may be stored
contiguously in a block of memory or one or more cache line(s)
8098.
[0728] The idea can also be applied to hierarchies that use
oriented bounding boxes (OBB) which are typically used to speed up
rendering of hair primitives. In order to illustrate one particular
embodiment, the memory reductions in a typical case of a standard
8-wide BVH over triangles will be evaluated.
[0729] The layout of an 8-wide BVH node 8100 is represented in the
following core sequence:
TABLE-US-00021 struct BVH8Node { float lowerX[8], upperX[8]; // 8 x
lower and upper bounds in the X dimension float lowerY[8],
upperY[8]; // 8 x lower and upper bounds in the Y dimension float
lowerZ[8], upperZ[8]; // 8 x lower and upper bounds in the Z
dimension void *ptr[8]; // 8 x 64bit pointers to the 8 child nodes
or leaf data };
and requires 276 bytes of memory. The layout of a standard 8-wide
quantized Node may be defined as:
TABLE-US-00022 struct QBVH8Node { Vec3f start, scale; char
lowerX[8], upperX[8]; // 8 x byte quantized lower/upper bounds in
the X dimension char lowerY[8], upperY[8]; // 8 x byte quantized
lower/upper bounds in the Y dimension char lowerZ[8], upperZ[8]; //
8 x byte quantized lower/upper bounds in the Z dimension void
*ptr[8]; // 8 x 64bit pointers to the 8 child nodes or leaf data
};
and requires 136 bytes.
[0730] Because only quantized BVH nodes are used at the leaf level,
all children pointers will actually point to leaf data 8101A-8108A.
In one embodiment, by storing the quantized node 8100B and all leaf
data 8101B-8108B its children point to in a single continuous block
of memory 8098, the 8 child pointers in the quantized BVH node
8100B are removed. Saving the child pointers reduces the quantized
node layout to:
TABLE-US-00023 struct QBVH8NodeLeaf { Vec3f start, scale; // start
position, extend vector of the parent AABB char lowerX[8],
upperX[8]; // 8 x byte quantized lower and upper bounds in the X
dimension char lowerY[8], upperY[8]; // 8 x byte quantized lower
and upper bounds in the Y dimension char lowerZ[8], upperZ[8]; // 8
x byte quantized lower and upper bounds in the Z dimension };
which requires just 72 bytes. Due to the continuous layout in the
memory/cache 8098, the child pointer of the i-th child can now be
simply computed by:
childPtr(i)=addr(QBVH8NodeLeaf)+sizeof(QBVH8NodeLeaf)+i*sizeof(LeafDataTy-
pe).
[0731] As the nodes at lowest level of the BVH makes up for more
than half of the entire size of the BVH, the leaf-level only
compression described herein provide a reduction to
0.5+0.5*72/256=0.64.times. of the original size.
[0732] In addition, the overhead of having coarser bounds and the
cost of decompressing quantized BVH nodes itself only occurs at the
BVH leaf level (in contrast to all levels when the entire BVH is
quantized). Thus, the often quite significant traversal and
intersection overhead due to coarser bounds (introduced by
quantization) is largely avoided.
[0733] Another benefit of the embodiments of the invention is
improved hardware and software prefetching efficiency. This results
from the fact that all leaf data is stored in a relatively small
continuous block of memory or cache line(s).
[0734] Because the geometry at the BVH leaf level is spatially
coherent, it is very likely that all primitives which are
referenced by a QBVH8NodeLeaf node share common properties/features
such as objectID, one or more vertices, etc. Consequently, one
embodiment of the invention further reduces storage by removing
primitive data duplication. For example, a primitive and associated
data may be stored only once per QBVH8NodeLeaf node, thereby
reducing memory consumption for leaf data further.
[0735] The effective bounding of hair primitives is described below
as one example of significant memory reductions realized by
exploiting common geometry properties at the BVH leaf level. To
accurately bound a hair primitive, which is a long but thin
structure oriented in space, a well-known approach is to calculate
an oriented bounding box to tightly bound the geometry. First a
coordinate space is calculated which is aligned to the hair
direction. For example, the z-axis may be determined to point into
the hair direction, while the x and y axes are perpendicular to the
z-axis. Using this oriented space a standard AABB can now be used
to tightly bound the hair primitive. Intersecting a ray with such
an oriented bound requires first transforming the ray into the
oriented space and then performing a standard ray/box intersection
test.
[0736] A problem with this approach is its memory usage. The
transformation into the oriented space requires 9 floating point
values, while storing the bounding box requires an additional 6
floating point values, yielding 60 bytes in total.
[0737] In one embodiment of the invention, the BVH compressor 8025
compresses this oriented space and bounding box for multiple hair
primitives that are spatially close together. These compressed
bounds can then be stored inside the compressed leaf level to
tightly bound the hair primitives stored inside the leaf. The
following approach is used in one embodiment to compress the
oriented bounds. The oriented space can be expressed by three
normalized vectors v.sub.x, v.sub.y, and v.sub.z that are
orthogonal to each other. Transforming a point p into that space
works by projecting it onto these axes:
p.sub.x=dot(v.sub.x,p)
p.sub.y=dot(v.sub.y,p)
p.sub.z=dot(v.sub.z,p)
[0738] As the vectors v.sub.x, v.sub.y, and v.sub.z are normalized,
their components are in the range [-1,1]. These vectors are thus
quantized using 8-bit signed fixed point numbers rather than using
8-bit signed integers and a constant scale. This way quantized
v.sub.x', v.sub.y', and v.sub.y' are generated. This approach
reduces the memory required to encode the oriented space from 36
bytes (9 floating point values) to only 9 bytes (9 fixed point
numbers with 1 byte each).
[0739] In one embodiment, memory consumption of the oriented space
is reduced further by taking advantage of the fact that all vectors
are orthogonal to each other. Thus, only two vectors (e.g.,
p.sub.y' and p.sub.z') are stored and p.sub.x'=cross(p.sub.y',
p.sub.z') can be determined, further reducing the required storage
to only six bytes.
[0740] What remains is quantizing the AABB inside the quantized
oriented space. A problem here is that projecting a point p onto a
compressed coordinate axis of that space (e.g., by calculating
dot(v.sub.x', p)) yields values of a potentially large range (as
values p are typically encoded as floating point numbers). For that
reason floating point numbers would be used to encode the bounds,
reducing potential savings.
[0741] To solve this problem, one embodiment of the invention first
transforms the multiple hair primitive into a space, where its
coordinates are in the range [0, 1/ 3]. This may be done by
determining the world space axis aligned bounding box b of the
multiple hair primitives, and using a transformation T that first
translates by b.lower to the left, and then scales by
1/max(b.size.x, b.size.y.b.size.z) in each coordinate:
T .function. ( p ) = 1 3 .times. ( p - b . lower ) / max .function.
( b . size . x , .times. b . size . y , b . size . z )
##EQU00001##
[0742] One embodiment ensures that the geometry after this
transformation stays in the range [0, 1/ 3] as then a projection of
a transformed point onto a quantized vector p.sub.x', p.sub.y', or
p.sub.z' stays inside the range [-1,1]. This means the AABB of the
curve geometry can be quantized when transformed using T and then
transformed into the quantized oriented space. In one embodiment,
8-bit signed fixed point arithmetic is used. However, for precision
reasons 16-bit signed fixed point numbers may be used (e.g.,
encoded using 16 bit signed integers and a constant scale). This
reduces the memory requirements to encode the axis-aligned bounding
box from 24 bytes (6 floating point values) to only 12 bytes (6
words) plus the offset b.lower (3 floats) and scale (1 float) which
are shared for multiple hair primitives.
[0743] For example, having 8 hair primitives to bound, this
embodiment reduces memory consumption from 8*60 bytes=480 bytes to
only 8*(6+12)+3*4+4=160 bytes, which is a reduction by 3.times..
Intersecting a ray with these quantized oriented bounds works by
first transforming the ray using the transformation T, then
projecting the ray using quantized v.sub.x', v.sub.y', and
v.sub.z'. Finally, the ray is intersected with the quantized
AABB.
[0744] The fat leaves approach described above provides an
opportunity for even more compression. Assuming there is an
implicit single float3 pointer in the fat BVH leaf, pointing to the
shared vertex data of multiple adjacent GridPrims, the vertex in
each grid primitive can be indirectly addressed by byte-sized
indices ("vertex_index_*"), thereby exploiting vertex sharing. In
FIG. 78, vertices 7801-7802 are shared--and stored in full
precision. In this embodiment, the shared vertices 7801-7802 are
only stored once and indices are stored which point to an array
containing the unique vertices. Thus, instead of 48 bytes only 4
bytes are stored per timestamp. The indices in the following code
sequence are used to identify the shared vertices.
TABLE-US-00024 struct GridPrimMBIndexed { PrimLeafDesc leafDesc; //
4B uint32_t primIndex; // 4B uint8_t vertex_index_time0[4]; // 4B
uint8_t vertex_index_time1[4]; // 4B // total 16 bytes up to here
struct { exp : 5; // shared exponent disp_x : 5; disp_y : 5; disp_z
: 5; }disp_mag_time0[16],disp_mag_time1[16]; // 80 bytes }; // 96
bytes total
[0745] In one embodiment, shared edges of primitives are only
evaluated once to conserve processing resources. In FIG. 79, for
example, it is assumed that a bounding box consists of the
highlighted quads. Rather than intersecting all triangles
individually, one embodiment of the invention performs ray-edge
computations once for each of the three shared edges. The results
of the three ray-edge computations are thus shared across the four
triangles (i.e., only one ray-edge computation is performed for
each shared edge). In addition, in one embodiment, the results are
stored to on-chip memory (e.g., a scratch memory/cache directly
accessible to the intersector unit).
Atomics for Graphics and Data Structures
[0746] An "atomic" is a set of operations which must be completed
as a single unit. Certain atomics would be beneficial for graphics
processing performance, especially when executing compute shaders.
One embodiment of the invention includes a variety of new atomics
to improve graphics processing performance, including: [0747]
Atomics that clamp [0748] `z-tested` atomic writes [0749]
`z-tested` atomic accumulation [0750] Atomics for ring-buffers
I. Atomics for Clamping
[0751] One embodiment of a clamping atomic specifies a destination,
type value, and minimum and maximum clamping values. By way of
example, a clamping atomic may take the form:
InterlockedAck/Clamp(destination, type value, type min, type max)
The above clamping operation atomically adds a value to the
destination and then clamps to the specified minimum and maximum
values (e.g., setting to the maximum for any values above the
maximum and setting to the minimum for any values below the
minimum).
[0752] Clamping atomic values may be 32 bits, 64 bits, or any other
data size. Moreover, clamping atomics may operate on various data
types including, but not limited to, uint, float, 2xfp16, float2,
and 4xfp16.
II. "Z-Tested" Scattered Writes
[0753] Z-tested scattered writes may be used for a variety of
applications including, for example: [0754] scattered cube map
rendering/voxelization (e.g., for environment probes); [0755]
scattered imperfect reflective shadow maps (RSMs) (similar to
imperfect shadow maps but for indirect illumination); and [0756]
dynamic diffuse global illumination style global illumination
through scattered "environment probe" updates.
[0757] The following is an example of a compare exchange
instruction which may be executed in one embodiment of the
invention: [0758] InterlockedCmpXChg_type_cmp_op( ) [0759]
type=int, uint, float [0760] cmp_op=less, greater, equal,
less_equal, greater_equal, not_equal [0761] e.g.:
InterlockedDepthCmpXChg_float_less_equal( )
[0762] An example 64-bit destination register 8201 is illustrated
in FIG. 82A storing a 32-bit depth value 8202 and a 32-bit payload
8203. In operation, the above compare exchange command only
exchanges payload and depth if the new floating point depth value
is less than or equal to the stored float value. In one embodiment,
the cmpxchg atomics are "remote" atomics, meaning that the actual
compare and atomic update is not done by the EU which issued the
instruction, but instead by a logic block close to the LLC (or
memory controller) storing the data.
Example High Level Shading Language (HLSL) Intrinsics for
Read-Write Byte Address Buffers (RWByteAddressBuffers)
[0763] In one embodiment, only the HighCompValue is of the type to
be compared with the high 32 bits in the 64 bit destination. The
rest are assumed to be converted to 32-bit unsigned integer
(asuint( ): [0764] void
RWByteAddressBuffer::InterlockedCompareHighExchange_Less(uint
byteAddress64, uint uHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0765] void
RWByteAddressBuffer::InterlockedCompareHighExchange_LessEqual(uint
byteAddress64, uint uHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0766] void
RWByteAddressBuffer::InterlockedCompareHighExchange_Greater(uint
byteAddress64, uint uHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0767] void
RWByteAddressBuffer::InterlockedCompareHighExchange_GreaterEqual(uint
byteAddress64, uint uHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0768] void
RWByteAddressBuffer::InterlockedCompareHighExchange_Equal(uint
byteAddress64, uint uHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0769] void
RWByteAddressBuffer::InterlockedCompareHighExchange_NotEqual(uint
byteAddress64, uint uHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0770] void
RWByteAddressBuffer::InterlockedCompareHighExchange_Less(uint
byteAddress64, int iHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0771] void
RWByteAddressBuffer::InterlockedCompareHighExchange_LessEqual(uint
byteAddress64, int iHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0772] void
RWByteAddressBuffer::InterlockedCompareHighExchange_Greater(uint
byteAddress64, int iHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0773] void
RWByteAddressBuffer::InterlockedCompareHighExchange_GreaterEqual(uint
byteAddress64, int iHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0774] void
RWByteAddressBuffer::InterlockedCompareHighExchange_Equal(uint
byteAddress64, int iHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0775] void
RWByteAddressBuffer::InterlockedCompareHighExchange_NotEqual(uint
byteAddress64, int iHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0776] void
RWByteAddressBuffer::InterlockedCompareHighExchange_Less(uint
byteAddress64, float fHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0777] void
RWByteAddressBuffer::InterlockedCompareHighExchange_LessEqual(uint
byteAddress64, float fHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0778] void
RWByteAddressBuffer::InterlockedCompareHighExchange_Greater(uint
byteAddress64, float fHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0779] void
RWByteAddressBuffer::InterlockedCompareHighExchange_GreaterEqual(uint
byteAddress64, float fHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0780] void
RWByteAddressBuffer::InterlockedCompareHighExchange_Equal(uint
byteAddress64, float fHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0781] void
RWByteAddressBuffer::InterlockedCompareHighExchange_NotEqual(uint
byteAddress64, float fHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal)
Example HLSL Intrinsics for Destination R
[0782] HighCompValue is of the type to be compared with the high 32
bits at the 64 bit dest. The rest is assumed to be converted using
asuint( )
[0783] All these instrinsics take a `dest` parameter of type `R`
which can either be a resource variable or a shared memory
variable. A resource variable is a scalar reference to a resource
including indexing or field references. A shared memory variable is
one defined with the `groupshared` keyword. In either case, the
type must be uint2 or uint64. When `R` is a shared memory variable
type, the operation is performed on the `value` parameter and the
shared memory register referenced by `dest`. When `R` is a resource
variable type, the operation is performed on the `value` parameter
and the resource location referenced by `dest`. The result is
stored in the shared memory register or resource location
referenced by `dest`: [0784] void
InterlockedCompareHighExchange_Less(R dest, uint uHighCompVal,
uint2 HighAndLowVal, out uint2 HighAndLowOrgVal) [0785] void
InterlockedCompareHighExchange_LessEqual(R dest, uint uHighCompVal,
uint2 HighAndLowVal, out uint2 HighAndLowOrgVal) [0786] void
InterlockedCompareHighExchange_Greater(R dest, uint uHighCompVal,
uint2 HighAndLowVal, out uint2 HighAndLowOrgVal) [0787] void
InterlockedCompareHighExchange_GreaterEqual(R dest, uint
uHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0788] void InterlockedCompareHighExchange_Equal(R dest, uint
uHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0789] void InterlockedCompareHighExchange_NotEqual(R dest, uint
uHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0790] void InterlockedCompareHighExchange_Less(R dest, int
iHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0791] void InterlockedCompareHighExchange_LessEqual(R dest, int
iHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0792] void InterlockedCompareHighExchange_Greater(R dest, int
iHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0793] void InterlockedCompareHighExchange_GreaterEqual(R dest, int
iHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0794] void InterlockedCompareHighExchange_Equal(R dest, int
iHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0795] void InterlockedCompareHighExchange_NotEqual(R dest, int
iHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0796] void InterlockedCompareHighExchange_Less(R dest, float
fHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0797] void InterlockedCompareHighExchange_LessEqual(R dest, float
fHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0798] void InterlockedCompareHighExchange_Greater(R dest, float
fHighCompVal, uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
[0799] void InterlockedCompareHighExchange_GreaterEqual(R dest,
float fHighCompVal, uint2 HighAndLowVal, out uint2
HighAndLowOrgVal) [0800] void
InterlockedCompareHighExchange_Equal(R dest, float fHighCompVal,
uint2 HighAndLowVal, out uint2 HighAndLowOrgVal) [0801] void
InterlockedCompareHighExchange_NotEqual(R dest, float fHighCompVal,
uint2 HighAndLowVal, out uint2 HighAndLowOrgVal)
III. "Z-Tested" Scattered Accumulation
[0802] Two embodiments are described below with respect to FIGS.
82B-C. FIG. 82B illustrates a 64-bit destination register storing a
32-bit depth value and a 32-bit payload value. FIG. 82C illustrates
a 64-bit destination storing a 32-bit depth value and two 16-bit
floating point values. The following is an example atomic: [0803]
InterlockedCmpAdd_type1_type2 cmp_op( ) [0804] type1=int, uint,
float [0805] type2=int, uint, float, 2xfp16 [0806] cmp_op=less,
greater, equal, less_equal, greater_equal, not_equal [0807] e.g.:
InterlockedCmpAccum_float_2xfp16_less( ) [0808] if the new float
depth value is < the stored float depth value: [0809] 1.
Exchange the stored depth value with the new one [0810] 2.
Dest.Payload.lowfp16+=InputPayload.lowfp16 [0811] 3.
Dest.Payload.highfp16+=InputPayload.highfp16
New HLSL Intrinsics for RWByteAddressBuffers
[0812] Only the HighCompValue is of the type to be compared with
the high 32 bits at the 64 bit destination. The AddLowVal can be of
type `float`, `int`, `uint` and `min16float2`:
[0813] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow Less(uint
byteAddress64, uint uHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0814] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_LessEqual(uint
byteAddress64, uint uHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0815] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_Greater(uint
byteAddress64, uint uHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0816] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_GreaterEqual(ui-
nt byteAddress64, uint uHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0817] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_Equal(uint
byteAddress64, uint uHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0818] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_NotEqual(uint
byteAddress64, uint uHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0819] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_Less(uint
byteAddress64, int iHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0820] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_LessEqual(uint
byteAddress64, int iHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0821] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_Greater(uint
byteAddress64, int iHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0822] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_GreaterEqual(ui-
nt byteAddress64, int iHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0823] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_Equal(uint
byteAddress64, int iHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0824] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_NotEqual(uint
byteAddress64, int iHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0825] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_Less(uint
byteAddress64, float fHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0826] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_LessEqual(uint
byteAddress64, float fHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0827] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_Greater(uint
byteAddress64, float fHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0828] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_GreaterEqual(ui-
nt byteAddress64, float fHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0829] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_Equal(uint
byteAddress64, float fHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0830] void
RWByteAddressBuffer::InterlockedCompareExchangeHighAddLow_NotEqual(uint
byteAddress64, float fHighCompVal, type AddLowVal, out uint2
HighAndLowOrgVal) [0831] Suggested new HLSL intrinsics for
destination R
[0832] Only the HighCompValue is of the type to be compared with
the high 32 bits at the 64 bit dest. The AddLowVal can be of type
`float`, `int`, `uint` and `min16float2`: [0833] void
InterlockedCompareExchangeHighAddLow_LessEqual(R dest, uint
uHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0834]
void InterlockedCompareExchangeHighAddLow_Greater(R dest, uint
uHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0835]
void InterlockedCompareExchangeHighAddLow_GreaterEqual(R dest, uint
uHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0836]
void InterlockedCompareExchangeHighAddLow_Equal(R dest, uint
uHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0837]
void InterlockedCompareExchangeHighAddLow_NotEqual(R dest, uint
uHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0838]
void InterlockedCompareExchangeHighAddLow_Less(R dest, int
iHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0839]
void InterlockedCompareExchangeHighAddLow_LessEqual(R dest, int
iHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0840]
void InterlockedCompareExchangeHighAddLow_Greater(R dest, int
iHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0841]
void InterlockedCompareExchangeHighAddLow_GreaterEqual(R dest, int
iHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0842]
void InterlockedCompareExchangeHighAddLow_Equal(R dest, int
iHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0843]
void InterlockedCompareExchangeHighAddLow_NotEqual(R dest, int
iHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0844]
void InterlockedCompareExchangeHighAddLow_Less(R dest, float
fHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0845]
void InterlockedCompareExchangeHighAddLow_LessEqual(R dest, float
fHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0846]
void InterlockedCompareExchangeHighAddLow_Greater(R dest, float
fHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal) [0847]
void InterlockedCompareExchangeHighAddLow_GreaterEqual(R dest,
float fHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal)
[0848] void InterlockedCompareExchangeHighAddLow_Equal(R dest,
float fHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal)
[0849] void InterlockedCompareExchangeHighAddLow_NotEqual(R dest,
float fHighCompVal, type AddLowVal, out uint2 HighAndLowOrgVal)
IV. Atomics for Ring Buffers
[0850] A ring buffer (or circular buffer) is a data structure
comprising a single, fixed-size buffer which operates as if it were
connected end-to-end. Circular buffers are commonly used for
buffering data streams. One embodiment of the invention includes
atomics for appending and popping entries to and from ring
buffers.
[0851] Initially AppendIndex and PopFrontIndex are 0. In order to
atomically append or pop, one embodiment uses special 64-bit
atomics. With these atomics, GPU threads can, for example,
implement a producer-consumer scheme within the limits of the
capacity of the ring buffer. A hardware watchdog can wake up
kernels that wait on the ring buffer.
[0852] The following code sequences illustrate atomic operation for
appending and popping entries from a ring buffer in accordance with
one embodiment of the invention:
a. Ring Buffer Append
TABLE-US-00025 InterlockedAppend( in dest64, in RingSize, out
AppendIndexOut ) atomically execute ( if( ( (dest64.AppendIndex+1)
% RingSize) != ( dest64.PopFrontIndex % RingSize) ) {
AppendIndexOut = dest64.AppendIndex; ++dest64.AppendIndex; } else {
AppendIndexOut = 0xffffffff; // error, ring-buffer full } )
b. Ring Buffer PopFront
TABLE-US-00026 InterlockedPopFront( in dest64, in RingSize, out
PopIndexOut ) atomically execute ( if( ( (dest64.PopFrontIndex) %
RingSize ) != ( dest64.AppendIndex % RingSize) ) { PopIndexOut =
dest64.PopFrontIndex; ++dest64.PopFrontIndex; } else { PopIndexOut
=0xffffffff; // error ring buffer empty } )
c. Example Use Cases [0853] i. Initialize the ringbuffer with
available number of entries using InterlockedAppend [0854] ii. A
number of threads run and temporarily pick/allocate entries using
Interlocked Pop Front [0855] iii. Entries get returned to the ring
buffer using InterlockedAppend [0856] iv. Threads can decide not to
wait for entries and deal with this case Pseudo code for a
multi-producer sample and a multi-consumer sample are illustrated
in FIGS. 84-85.
[0857] A producer pseudo code sample is illustrated in FIG. 84A.
For this example, assume the job_entry_ready_buffer is initialized
to all zeros and the job_entry_consumed_buffer is initialized to
all 1s:
[0858] A consumer pseudo code sample is illustrated in FIG. 84B.
For this example, it is assumed that the job_entry_ready_buffer is
initialized to all zeros and the job_entry_consumed_buffer is
initialized to all 1s.
[0859] FIG. 83A illustrates an example ring buffer implemented in
accordance with one embodiment. A ring buffer pop back operation is
shown in which entries N, N+1, etc., where N is an integer value,
are popped and stored in ring buffer entries 0, 1, etc. FIG. 83B
illustrates a 64-bit destination register 8211 storing the append
index value 8212 and the pop front index value 8213, in accordance
with the following code sequence:
TABLE-US-00027 InterlockedPopBack( in dest64, in RingSize, out
PopIndexOut ) atomically execute ( if( ( (dest64.PopFrontIndex) %
RingSize ) != ( ciest64.Appendindex % RingSize) ) { PopIndexOut =
dest64.Appendindex; --dest64.AppendIndex; } else { PopIndexOut =
0xffffffff; // error ring buffer empty } )
V. Atomic Multiplication Operations
[0860] One embodiment of a multiply atomic specifies a destination
and a type value. By way of example, a multiply atomic may take the
form:
[0861] InterlockedMultiply(destination, type value)
[0862] In one embodiment, the multiply operation atomically
multiplies a value of a specified data type with the value in the
destination, which may be the same data type or a different data
type.
[0863] Multiply atomic values may be, by way of example and not
limitation, 4-bit, 8-bit, 16-bit, 32-bit, and 64-bit integers and
16-bit, 32-bit, and 64-bit floating point values. The values may be
signed or unsigned. Moreover, a number of parallel multiply
operations may be performed based on the smallest data element
size. For example, floating point multiplication circuitry may be
configured to perform a single 32-bit floating point multiplication
or dual 16-bit floating point multiplications. Formats such as
Bfloat16 or TensorFloat16 may be used to efficiently perform the
parallel multiplications. Similarly, an integer multiplier may be
capable of performing a single 32-bit multiplication, dual 16-bit
multiplications, four 8-bit multiplications, or eight 4-biut
multiplications. Various other types of data formats and parallel
operations may be used while still complying with the underlying
principles of the invention including, for example, 2.times.FP16,
float2, 4.times.FP16, 11_11_10 FP and 2.times.11_11_10 FP.
[0864] These atomics may be used for a variety of purposes
including machine learning operations, Weighted Blended Order
Independent Transparency (OIT) or Opacity Shadow Maps.
Apparatus and Method for Graphics Processor-Managed Tiled
Resources
[0865] One embodiment of the invention improves the efficiency with
which a user-written GPU program can cache and reuse data stored in
a buffer or texture. This embodiment also provides for a logical
representation of large, procedurally-computed resources that may
or may not physically fit into the GPU memory at the same time.
[0866] In one embodiment of the invention, a new tiled resource is
defined and managed by the GPU, referred to herein as a GPU managed
tiled resource or a GPU managed buffer. In one implementation, the
buffer or other tiled storage resource contains up to N fixed sized
blocks of memory, where N is an integer value. Different GPU
architectures may support a different maximum number of blocks
(N).
[0867] In one embodiment, the GPU-managed tiled resource is used to
efficiently share data between shaders--i.e., where one shader acts
as a "producer" for one or more "consumer" shaders. For example,
the producer shader may generate procedurally-updated content which
the consumer shader may use without involving interaction with the
CPU. As another example, in ray tracing implementations, various
forms of skinning animation may need to be updated on traversal.
One shader may skin a small portion of the mesh, storing results in
the tiled resource, without CPU intervention. As other rays trace
the same portion, they can access the data locally from the tiled
resource, without accessing main memory.
[0868] FIG. 85A illustrates one embodiment of an architecture for
implementing GPU-managed tiled resources 8531. A graphics processor
8521 includes a scheduler 8510 for scheduling shaders 8511A-B on
the set of execution units 4001. Execution of the shaders requires
access to tiled resources 8531 which are managed by a resource
manager 8512. In the example provided below, one shader 8511A is
designated as a "producer", storing its results in the tiled
resource 8531, and the other shader 85118 is a "consumer," using
the results generated by the producer shader 8511A. Consequently,
the producer shader 8511A needs access to write to the tiled
resource 8531 and the consumer shader 85118 needs read access to
the tiled resource 8531. It should be noted, however, that a
producer/consumer architecture is not required for complying with
the underlying principles of the invention.
[0869] In one implementation, the tiled resource 8531 comprises an
on-chip tile memory or tile buffer, which stores tile-sized blocks
0-(N-1) of data. The "tile" size may be variable based on the
architecture of the graphics processor 8521 and the configuration
of the graphics processing pipeline. In one embodiment, the
graphics processing pipeline is configured to perform tile-based
deferred rendering, tile-based immediate mode rendering, and/or
other form of tile-based graphics processing, using the tiled
resource 8531.
[0870] In one embodiment, an execution unit (EU) 4001 or other
processing unit, requests a block using a hash value or other form
of ID 8501 (e.g., a 64-bit hash in one embodiment). A resource
manager 8512 determines whether the block exists within the tiled
resource 8531 comprising N fixed sized blocks. If no such block is
found, the buffer manager 8510 evicts the least recently used (LRU)
block or selects an unused block if one exists. The response 8502
identifies the allocated block which the buffer manager 8510 marks
as "used" with the given hash value. In one implementation, a flag
is also returned indicating that the block is new. A least recently
used block which is replaced loses the old content which it stored.
If the block is already there, a flag is returned that indicates
the block already exists and it is returned nevertheless.
[0871] While illustrated as a component within the graphics
processor 8521, the tiled resource 8531 may be implemented within a
memory external to the graphics processor 8521 such as a system
memory or system-level cache.
[0872] Certain classes of shaders 8511A-B which execute on the EUs
4001 of a GPU are a priori known to require a block of memory. For
example, these shaders may always execute in the lanes of a wave.
In one embodiment, the scheduler 8510 which schedules the execution
of these shaders 8511A-B constructs a 64 bit ID/Hash from
system-generated values. For example, one embodiment, in the
context of raytracing, uses the InstanceID and the GeometryID to
construct a unique 64-bit hash. However, a variety of other system
generated variables may be used.
[0873] In this embodiment, the scheduler 8510 checks via the
resource manager 8512 whether there is already a block of the tiled
resource 8531 allocated for the 64 bit hash. If so, the shader
8511A-B is executed under the assumption that the block already
contains cached data and that this can be consumed by the shader
and the shader is scheduled on the EUs 4001. The resource manager
8512 locks the block of memory from being reused as long as the
shader that uses the data cached lockin that block is executing. As
the shader is executed by one or more EUs 4001, it updates the
block in the tiled resource 8531 using the block ID 8501 and, for
certain operations, receives responses 8502 from the resource
manager 8512.
[0874] In one embodiment, if the scheduler 8510 initially finds
that there is no block with the given 64-bit hash, the resource
manager 8512 locates an unused block or uses the least recently
used block (or other block) that has already allocated and isn't
currently in use. If it cannot locate such a block, it may postpone
execution of the shader until such a block becomes available. When
a block is available, the tiled resource manager 8512 locks the
tiled resource block from being reused as long as the shader is
executing and schedules the shader. A flag may be passed to the
shader to indicate that the block is empty and that the shader can
use it to generate and store data. After writing data to the tiled
resource block, the shader may continue execution as if the tiled
resource block with its data had already been available.
[0875] Returning to the consumer/producer example above, a producer
shader 8511A may be scheduled to generate a novel block or tile of
the procedural resource 8531 if the requested hash is not valid in
the pool. Such a requested hash may be generated by one or more
consumer shaders 8511B, which the resource manager 8512 would block
until their request is filled.
[0876] In one embodiment, tiled resource blocks are evicted to a
solid-state device 8515 or other high speed storage medium. The SSD
8515 or other storage device may be integrated locally on the same
substrate and/or card as the graphics processor 8521 and may be
configured to save tiled resource blocks and other data during
internal graphics processor 8521 context switches.
[0877] A method in accordance with one embodiment is illustrated in
FIG. 85B. The method may be implemented within the context of the
architectures described above, but is not limited to any particular
architecture.
[0878] At 8551 the scheduler evaluates the next shader to be
scheduled for execution and, at 8552, determines a hash ID to be
used to identify the tiled resource block (e.g., using one or more
of the techniques described herein). At 8553, the scheduler queries
the tiled resource manager with the hash ID.
[0879] If a block is already allocated for this hash ID, determined
at 8554, then the tiled resource manager locks the tiled resource
block at 8555 and the shader uses the tiled resource block during
execution at 8556. The tiled resource block may subsequently be
unlocked when the shader completes, unless it is locked with a hash
ID of a consumer shader that will require the data after the
current (producer) shader completes. In any case, the process
returns to 8551 for scheduling of the next shader.
[0880] If, at 8554, no tiled resource block is identified with the
hash ID, then the tiled resource manager assigns a tiled resource
block to the hash ID and may allocate a flag to the shader
indicating that it may use this tiled resource block. As mentioned,
the tiled resource manager may evict existing data from a tiled
resource block to assign the tiled resource block to the current
shader. The tiled resource block is locked at 855 and the shader
uses the tiled resource block during execution at 8556.
[0881] The GPU-managed tiled buffer 8531 may be used in a variety
of ways. For example, a SIMD wave of lanes want to enter the same
intersection shader box bundled by bindless tread dispatcher
(described below). Before the intersection shader is run, the
hardware requests a block from the buffer manager 8510.
[0882] The 64-bit hash may be generated in different ways. For
example, in one embodiment, the 64-bit hash is the InstanceID of
the current ray traversal instance combined with the frame counter.
If the block is new, the hardware may launch a user compute shader
running within the lanes of the wave that then fills the block
(e.g., with skinned triangles). If the block is old, then the
shader may not be launched. An intersection shader is then executed
and is provided with the pointer to the block. The intersection
shader may then perform ray/triangle intersections and/or support
may be provided for a hardware instruction for the ray/triangle
intersections (as described herein). Alternatively, the block may
be designed to only contain triangles. In this case, the hardware
iterates over these triangles (without building a BVH over them)
and may, for example, update closest hit shaders or call into
any-hit shaders. Various other use cases may take advantage of the
GPU-managed tiled resource 8531 as described above.
Apparatus and Method for Efficient Lazy BVH Build
[0883] Complex dynamic scenes are challenging for real-time ray
tracing implementations. Procedural surfaces, skinning animations,
etc., require updates of triangulation and accelerating structures
in each frame, even before the first ray is launched.
[0884] Lazy builds evaluate scene elements "on-demand", as driven
by ray traversal. The rendering of a frame starts with a coarse
acceleration structure like a scene-graph or hierarchies of the
previous frame, then progressively builds the newly required
acceleration structures for the objects that are hit by rays during
traversal. Invisible objects can be effectively excluded from the
construction process. However, these techniques are not easily
implemented with current systems and APIs, because the higher-level
(i.e., per-object) programmability essential for computing the
instance visibility is not supported.
[0885] One embodiment of the invention supports a multi-pass lazy
build (MPLB) for real-time ray tracing that resolves these problems
with an extended programming model. It allows the instance-level
traversal to be tracked during each ray dispatch and selectively
builds bottom level acceleration structures (BLASs) for only the
potentially visible geometry at render time. Akin to some adaptive
sampling techniques, MPLB as described herein may require multiple
ray dispatches over the same set of pixels to relaunch rays to
previously unbuilt parts of the scene, but certain embodiments of
the invention include techniques to minimize this overhead, such as
the assumption of frame-to-frame coherence and rasterized primary
visibility. These techniques can provide a significant reduction in
build complexity compared to one-time builders with only a marginal
increase in traversal cost on average.
[0886] FIG. 86A illustrates one embodiment of an on-demand (or
"lazy") builder 8607 for performing lazy build operations as
described herein. In addition, this embodiment includes traversal
suspension circuitry/logic 8620 for suspending ray traversal. The
ray traversal suspension circuitry/logic 8620 may be implemented in
hardware, software, or any combination thereof. Ray stack storage
8605 stores suspended ray stacks 8610 when traversal is suspended
(as described in greater detail herein). In addition, GPU-side
command scheduling launches lazy build tasks and ray continuations
on execution units 4001 without supervision by the CPU. Traversal
atomics are also used to reduce shader overhead.
Traversal Suspension Upon Missing Bottom Level Acceleration
Structure (BLAS) Encounter
[0887] In one implementation, using a programming model with a
traversal shader extension, missing instances (e.g., missing bottom
level acceleration structures of the BVH 8005) are programmatically
marked, so that they can be identified and updated in a separate
pass. Then either an incomplete traversal is performed or traversal
is aborted.
[0888] To render the final pixels, the primary shader of the
corresponding pixel may need to be relaunched, leading to several
repeated traversal and shader execution operations. In one
embodiment, traversal suspension logic 8620 backs up the entire ray
context 8610 (ray stack, continuations, etc.) into off-chip memory
8605 when traversal is suspended. In one embodiment, this traversal
suspension an intrinsic function which is managed by the driver
(e.g., SuspendTraversal( )); however, the underlying principles of
the invention are not limited to this implementation. In addition,
a new DispatchRay( ) variant in the host side--executed by the CPU
3199--re-schedules the suspended ray stacks from the ray context
8610 to continue traversal shader execution.
GPU-Side Command Scheduling for Build and Dispatch
[0889] Another significant overhead of current lazy build
implementations is the continuous requirement of CPU 3199 readback
and conditional scheduling of the BVH builder 8007 and ray
dispatching on the GPU 2505. To improve efficiency, in one
implementation, the BVH processing circuitry/logic 8004 runs the
BVH build asynchronously with the ray traversal 8003. Upon the
completion of the build tasks, the ray tracing engine 8000 executes
the ray dispatch to continue the suspended ray stacks from the ray
context 8610.
Traversal Atomics to Reduce Traversal Shader Overhead
[0890] One problem with current implementations is that if an
instance is missing (unbuilt), several rays may traverse it, and
mark it for the lazy builder 8607 to update it. A simple task that
could be done by just one traversal shader invocation is repeated
by hundreds or more invocations. The traversal shader is not
resource-intensive, but it has a significant overhead to launch,
perform input/output functions, and store results.
[0891] In one embodiment of the invention, unbuilt instance leaves
can be marked as "atomic" nodes. Atomic nodes can be traversed by
only one ray at once. An atomic node is locked once a ray traverses
it, and unlocked at the end of the traversal shader execution. In
one embodiment, the traversal shader sets the status of a node to
"invalid", which prevents rays entering it even after the lock is
released. This allows the traversal hardware to either skip the
node, or suspend the traversal of the ray, without executing a new
traversal shader.
[0892] In one embodiment, for atomics nodes, instead of regular
atomic semantics, certain mutex/condition semantics are used. For
example, if the traversal circuitry/logic 8003 traverses a ray to a
proxy node, it attempts to lock the node. If this fails as the node
is already locked, it automatically executes "suspendRay" without
returning to the EU 4001. If the locking is executed successfully,
the traversal circuitry/logic 8003 processes the proxy node.
Lazy Build of Acceleration Structures with a Traversal Shader
[0893] One embodiment of the invention operates in accordance with
the processing flow shown in FIG. 86B. By way of an overview, the
on-demand builder 8607 builds acceleration structures over geometry
instances 8660 determined to be potentially visible. The
potentially visible instances 8660 are generated by a pre-builder
8655 based on primary visibility data from the G-buffer 8650 and
visibility history data 8651 indicating visibility in the previous
frame. The potentially visible instances 8660 may also be
determined based on a visible bottom level acceleration structure
(BLAS) map 8675 which indicates the bottom level nodes of the
acceleration structure that include visible primitives. In one
embodiment, the visible BLAS map 8675 is continually updated in
response to traversal operations performed by the traversal logic
8670, which may include dedicated traversal circuitry and/or
traversal shaders executed on the execution units of the graphics
processor.
[0894] The on-demand builder 8607 generates those portions of the
acceleration structure which are associated with the potentially
visible instances 8660. A ray generation shader 8678 selectively
generates rays based on these portions of the acceleration
structure which the traversal unit 8670 traverses through the
acceleration structure portions. The traversal unit 8670 notifies
the on-demand builder 8607 of additional acceleration structure
nodes that the traversal unit 8670 requires for traversal. Also,
the traversal unit 8670 updates the BLAS pixel masks 8677 used by
the ray generation shader 8678 (e.g., which only generates rays for
unmasked pixels) and visible BLAS map 8675.
[0895] Thus, the on-demand builder 8607 selectively builds bottom
level acceleration structures over the potentially visible
instances 8660 and the instance visibility is updated during ray
traversal 8670. Unlike the previous implementations, the
embodiments of the invention operate in multiple passes in order to
avoid complicated ray scheduling. The idea is analogous to recent
texture-space shading approaches where visibility-driven marking of
texels is used to avoid redundant shading before the final
rendering.
[0896] In operation, the BLASes for empty instances that were
marked as potentially visible in the previous pass are first built.
In the second pass, the ray generation shader 8678 selectively
reshoots the rays to the unfinished pixels, where a traversal
shader is used to either record more potentially visible empty
instances or complete the pixel. The number of incomplete pixels
decreases after each iteration until there are no rays left that
traversed an empty instance.
[0897] One embodiment of the invention performs a hybrid rendering
using the GPU rasterizer and ray tracing hardware together. This is
because when creating the G-buffer 8650, the primary visibility of
all instances in the scene is easily obtained. Hence, the
pre-builder 8655 in these embodiments takes advantage of hybrid
rendering by efficiently constructing the initial acceleration
structure using this data. Before the first iteration, potentially
visible instances 8660 are marked in this pre-build heuristic (as
discussed below).
[0898] The code sequence below is an abstracted high level shader
language (HLSL) describing one embodiment of the traversal shader
described with some intrinsic- and user-functions:
TABLE-US-00028 RWStructuredBuffer<vblas> visibleBlasMap[ ] :
register(u0, space0); RWStructuredBuffer<pmask> pixelMasks[ ]
: register(u0, space1); [shader("traversal")] void
myVisibilityShader(in RayPayload rp) { uint2 index =
DispatchRaysIndex ( ) ; uint2 size = DispatchRaysDimensions ( ) ;
UpdateVisibility(visibleBlasMap, InstanceID( ), true) ; // Control
BLAS traversal with updating pixel mask
RaytracingAccelerationStructure myAccStructure; bool
isInstanceEmpty = IsEmptyInstance( ); if (isInstanceEmpty) {
UpdateMask(pixelMasks, index.y*size.x + index.x, false);
rp.trav_valid = false; skipTraversal ( ) ; } else if
(!isInstanceEmpty && !rp,trav_valid) skipTraversal ( ) ;
else { myAccStructure = FetchBLAS(InstanceID( ) ) ; RayDesc
transformedRay = { . . . }; // Set the next level instance and hit
shader table offset SetInstance(myAccStructure, transformedRay,
hitShaderOffset ) ; }
[0899] The SkipTraversal( ) intrinsic is defined to ignore the
current instance and continue traversal in the higher-level
acceleration structure. As mentioned, the visible bottom-level
acceleration structure (BLAS) map 8675 is used to record instance
visibility commonly used in acceleration structure builders and
traversal shaders. As shown in FIG. 86C, one embodiment of the
visible BLAS map 8675 contains a flag 8676 associated with each
BLAS ID 8674 indicating the BLAS visibility to which the instance
refers and two flags, Built_Full and Built_Empty, indicating
whether the BLAS has already been built. In addition, a boolean
flag, trav_valid, is added to the ray payload to keep track of
traversal status, which can be used for checking whether the ray
has encountered an empty instance thus far.
[0900] In one embodiment, the visibility in the traversal shader is
conservatively updated because all traversed instances are
potentially visible to the current ray. Hence, the first task is to
set the visibility flag as True for the corresponding BLAS of the
current instance. It also sets the visibility history (vis_history)
flag as True to reuse it in the next frame (line 9 of the above
code sequence). Next, the traversal destination is determined based
on the status of the current instance (empty or full) and the ray
status (i.e., the trav_valid value). This is classified into three
states 8690-8692 as shown in FIG. 86D.
[0901] For an empty instance 8690, the corresponding pixel mask is
reset (line 15) for reshooting rays in the next pass. The current
traversal is then invalidated by setting the trav_valid flag in the
ray payload (line 16). Finally, TLAS traversal continues by
invoking SkipTraversal( ).
[0902] For the full instance and invalid traversal case 8691, the
current instance has a built BLAS, but the ray has encountered an
empty instance so far (i.e., trav_valid is False). Because the ray
will be eventually shot again to the current pixel, the BLAS
traversal can be skipped (line 20).
[0903] For a full instance and valid traversal 8692, since the ray
normally traversed the acceleration structure without empty
instances, the traversal shader fetches the BLAS of the current
instance and continues the traversal. If the ray maintains validity
until the end of the traversal, the ray will normally invoke and
execute the closest-hit shader or miss shader.
[0904] Otherwise, the current pass is terminated, which prevents
the overheads of hardware ray traversal and shader launching for
secondary rays. In the next pass, the rays are shot again only to
the pixel having the "False" mask, and a valid traversal for those
pixels is attempted.
[0905] For the acceleration structure building operation, the
BLASes of the instances are built or empty instances are created,
depending on the visibility flag of the visibility bit mask. The
potentially visible instance normally constructs the BLAS
(BUILD_FULL), and the invisible instance computes only the bounding
box of the geometry and packs it in the leaf node of TLAS
(BUILD_EMPTY). The other two flags are also referred to, indicating
whether a BUILD_FULL or BUILD_EMPTY action was already performed
for the current object in the previous pass. By checking these
flags, duplicate actions can be avoided for the same object in the
different iterations of the Build-Traverse loop.
[0906] Once the BLAS build process for the objects is finished, the
final acceleration structure is constructed by building the TLAS
over these BLASes. The TLAS is rebuilt only in the first pass and
refitted in the rest of the passes because the bounding boxes of
all objects could be already set up in the first pass.
[0907] As described above, one embodiment of the invention performs
multiple passes, which makes it sometimes redundantly shoot rays
for the same pixel. This is because the current pass should make up
for the invalid traversal in the previous pass. This can lead to
redundant hardware ray traversal and shader invocations. However,
one embodiment limits this overhead of the traversal costs only to
the pixels corresponding to invalid traversal by applying a pixel
mask.
[0908] Moreover, different techniques are used to identify
potentially visible BLASes (and build them), even before the first
ray is traversed (e.g., by the pre-builder 8655). Using the
G-buffer 8650, directly visible instances that are likely to be
traversed by primary rays can be marked. Furthermore, there is
assumed to be a significant amount of frame-to-frame coherence;
thus, the BLASes of instances traversed in the previous frame are
also pre-built. The combination of these two techniques greatly
reduces the number of Build-Traverse iterations.
Apparatus and Method for a Material Culling Mask
[0909] Existing ray tracing APIs use an 8-bit cull mask to skip ray
traversal for certain geometry instances. This is used, for
example, to prevent specific objects from casting shadows, or to
hide objects from reflections. This feature allows different
subsets of geometry to be represented within a single acceleration
structure as opposed to building separate acceleration structures
for each subset. The bit settings in the 8-bit mask can be used to
balance traversal performance and the resource overhead for
maintaining multiple acceleration structures. For example, if a bit
in the mask is set to 0, the corresponding instance may be
ignored.
[0910] Rendering engines can associate multiple geometry instances
with an asset and each geometry instance can contain multiple
materials. However, current ray tracing APIs only allow
specification of the culling mask at the granularity of an
instance. This means that assets which have different culling masks
on different materials cannot use standard culling. As a
workaround, current implementations use any-hit shaders to ignore
intersections, which is expensive and complicated.
[0911] As illustrated in FIG. 87, one embodiment of the invention
exposes these masking controls on a per-material basis. In
particular, one implementation includes an N-bit material-based
cull mask 8701 to skip ray traversal for portions of geometry
instances associated with certain materials. In one embodiment, an
8-bit material-based cull mask is used, but the underlying
principles of the invention are not limited to this implementation.
In contrast to existing implementations, the material-based cull
mask 8701 is exposed and can be utilized by the traversal
circuitry/logic 8003 for instance culling on a per-material basis
as well as a per-instance basis.
[0912] In one specific implementation, the N-bit cull mask 8701 is
stored inside of a hit group 8700, providing fixed-function
per-material culling and alleviating the need for expensive any-hit
shader workarounds. A "hit group" 8700 as used herein is an API
object that contains a set of shaders used to process rays hitting
a given object in the scene. The set of shaders may include, for
example, a closest-hit shader, an any-hit shader, and (for
procedural geometry) an intersection shader. In one implementation,
the material-based cull mask 8701 is associated with the hit group
8700, as an additional piece of data.
[0913] To associate the cull mask 8701 with the hit group 8700, the
cull mask 8701 may be stored within the 32-byte shader record that
the API provides for the implementation to use (e.g., identified
via a record ID as described herein). Note, however, that the
underlying principles of the invention are not limited to any
particular technique for associating a cull mask with a hit
group.
[0914] In one embodiment, the traversal/intersection circuitry 8003
directly culls potential hits based on the material-based cull mask
8701. For example, a mask value of 0 may indicate that instances
with a corresponding material should be culled. Alternatively, or
in addition, this behavior can be emulated by injecting any-hit
shaders inside the driver.
Geometric Image Accelerator and Method
[0915] A geometry image is a mapping of a three dimensional (3D)
triangle mesh onto a two dimensional (2D) domain. In particular, a
geometry image may represent geometry as a 2D array of quantized
points. Corresponding image data such as colors and normals may
also be stored in 2D arrays using the same implicit surface
parametrization. The 2D triangle mesh represented by the 2D array
is defined by a regular grid of vertex positions with implicit
connectivity.
[0916] In one embodiment of the invention, a geometry image is
formed by mapping a 3D triangle mesh into a 2D plane, resulting in
an implied triangle connectivity defined by a regular grid of
vertex positions. The resulting 2D geometry image can be processed
in various ways within the graphics pipeline including
down-sampling and up-sampling using mipmaps.
[0917] As illustrated in FIG. 88, one embodiment of the invention
performs ray tracing by generating a quadtree structure 8855 over
the geometry image domain, where each quadtree node 8800, 8810-8813
stores an axis-aligned bounding box (AABB) over the vertex
positions of the 2D triangle mesh 8820. As illustrated, each node
8800, 8810-8813 stores the minimum and maximum coordinates of the
associated AABB which contains one or more of the triangles and/or
vertices. This results in a structure which is extremely
regularized and very easy to compute.
[0918] Once the AABBs are constructed over the 2D triangle mesh,
ray tracing operations may be performed using the AABBs as
described herein with respect to the various embodiments of the
invention. For example, traversal operations may be performed to
determine that a ray traverses one of the bottom-level nodes
8810-8813 of the BVH. The ray may then be tested for intersections
with the 2D mesh and hit results (if any) generated and processed
as described herein (e.g., in accordance with a material associated
with the 2D triangle mesh).
[0919] As illustrated, in one embodiment, storage/compression logic
8850 is configured to compress and/or store the AABBs as dual image
pyramids 8855, one storing the minimum values and one storing the
maximum values. In this embodiment, different compression schemes
developed for geometry images can be used to compress the minimum
and maximum image pyramids.
[0920] The quadtree structures 8855, 8810-8813 described above with
respect to FIG. 88 may be generated by the BVH builder 8007.
[0921] Alternatively, the quadtree structures may be generated by a
different set of circuitry and/or logic.
Apparatus and Method for Box-Box Testing and Accelerated Collision
Detection for Ray Tracing
[0922] FIG. 89A-B illustrate a ray tracing architecture in
accordance with one embodiment of the invention. A plurality of
execution units 8910 execute shaders and other program code related
to ray tracing operations. A "Traceray" function executed on one of
the execution units (EUs) 8910 triggers a ray state initializer
8920 to initialize the state required to trace a current ray
(identified via a ray ID/descriptor) through a bounding volume
hierarchy (BVH) (e.g., stored in a in a stack 5121 in a memory
buffer 8918 or other data structure in local or system memory
3198).
[0923] In one embodiment, if the Traceray function identifies a ray
for which a prior traversal operation was partially completed, then
the state initializer 8920 uses the unique ray ID to load the
associated ray tracing data 4902 and/or stacks 5121 from one or
more buffers 8918 in memory 3198. As mentioned, the memory 3198 may
be an on-chip/local memory or cache and/or a system-level memory
device.
[0924] As discussed with respect to other embodiments, a tracking
array 5249 may be maintained to store the traversal progress for
each ray. If the current ray has partially traversed a BVH, then
the state initializer 8920 may use the tracking array 5249 to
determine the BVH level/node at which to restart.
[0925] A traversal and raybox testing unit 8930 traverses the ray
through the BVH. When a primitive has been identified within a leaf
node of the BVH, instance/quad intersection tester 8940 tests the
ray for intersection with the primitive (e.g., one or more
primitive quads), retrieving an associated ray/shader record from a
ray tracing cache 8960 integrated within the cache hierarchy of the
graphics processor (shown here coupled to an L1 cache 8970). The
instance/quad intersection tester 8940 is sometimes referred to
herein simply as an intersection unit (e.g., intersection unit 5103
in FIG. 51).
[0926] The ray/shader record is provided to a thread dispatcher
8950, which dispatches new threads to the execution units 8910
using, at least in part, the bindless thread dispatching techniques
described herein. In one embodiment, the ray/box traversal unit
8930 includes the traversal/stack tracking logic 5248 described
above, which tracks and stores traversal progress for each ray
within the tracking array 5249.
[0927] A class of problems in rendering can be mapped to test box
collisions with other bounding volumes or boxes (e.g., due to
overlap). Such box queries can be used to enumerate geometry inside
a query bounding box for various applications. For example, box
queries can be used to collect photons during photon mapping,
enumerate all light sources that may influence a query point (or
query region), and/or to search for the closest surface point to
some query point. In one embodiment, the box queries operate on the
same BVH structure as the ray queries; thus the user can trace rays
through some scene, and perform box queries on the same scene.
[0928] In one embodiment of the invention, box queries are treated
similarly to ray queries with respect to ray tracing
hardware/software, with the ray/box traversal unit 8930 performing
traversal using box/box operations rather than ray/box operations.
In one embodiment, the traversal unit 8930 can use the same set of
features for box/box operations as used for ray/box operations
including, but not limited to, motion blur, masks, flags, closest
hit shaders, any hit shaders, miss shaders, and traversal shaders.
One embodiment of the invention adds a bit to each ray tracing
message or instruction (e.g., TraceRay as described herein) to
indicate that the message/instruction is associated with a BoxQuery
operation. In one implementation, BoxQuery is enabled in both
synchronous and asynchronous ray tracing modes (e.g., using
standard dispatch and bindless thread dispatch operations,
respectively).
[0929] In one embodiment, once set to the BoxQuery mode via the
bit, the ray tracing hardware/software (e.g., traversal unit 8930,
instance/quad intersection tester 8940, etc) interprets the data
associated with the ray tracing message/instruction as box data
(e.g., min/max values in three dimensions). In one embodiment,
traversal acceleration structures are generated and maintained as
previously described, but a Box is initialized in place of a Ray
for each primary StackID.
[0930] In one embodiment, hardware instancing is not performed for
box queries. However, instancing may be emulated in software using
traversal shaders. Thus, when an instance node is reached during a
box query, the hardware may process the instance node as a
procedural node. As the header of both structures is the same, this
means that the hardware will invoke the shader stored in the header
of the instance node, which can then continue the point query
inside the instance.
[0931] In one embodiment, a ray flag is set to indicate that the
instance/quad intersection tester 8940 will accept the first hit
and end the search (e.g., ACCEPT_FIRST_HIT_AND_END_SEARCH flag).
When this ray flag is not set, the intersected children are entered
front to back according to their distance to the query box, similar
to ray queries. When searching for the closest geometry to some
point, this traversal order significantly improves performance, as
is the case with ray queries.
[0932] One embodiment of the invention filters out false positive
hits using any hit shaders. For example, while hardware may not
perform an accurate box/triangle test at the leaf level, it will
conservatively report all triangles of a hit leaf node. Further,
when the search box is shrunken by an any hit shader, hardware may
return primitives of a popped leaf node as a hit, even though the
leaf node box may no longer overlap the shrunken query box.
[0933] As indicated in FIG. 89A, a box query may be issued by the
execution unit (EU) 8910 sending a message/command to the hardware
(i.e., Traceray). Processing then proceeds as described
above--i.e., through the state initializer 8920, the ray/box
traversal logic 8930, the instance/quad intersection tester 8940,
and the bindless thread dispatcher 8950.
[0934] In one embodiment, the box query re-uses the MemRay data
layout as used for ray queries, by storing the lower bounds of the
query box in the same position as the ray origin, the upper bounds
in the same position as the ray direction, and a query radius into
the far value.
TABLE-US-00029 struct MemBox { // 32 Bytes (semantics changed)
Vec3f lower; // the lower bounds of the query box Vec3f upper; //
the upper bounds of the query box float unused; float radius; //
additional extension of the query box (L0 norm) // 32 Bytes
(identical to standard MemRay) };
[0935] Using this MemBox layout, the hardware uses the box
[lower-radius, upper+radius] to perform the query. Therefore, the
stored bounds are extended in each dimension by some radius in L0
norm. This query radius can be useful to easily shrink the search
area, e.g. for closest point searches.
[0936] As the MemBox layout just reuses the ray origin, ray
direction, and T.sub.far members of the MemRay layout, data
management in hardware does not need to be altered for ray queries.
Rather, the data is stored in the internal storage (e.g., the ray
tracing cache 8960 and L1 cache 8970) like the ray data, and will
just be interpreted differently for box/box tests.
[0937] In one embodiment, the following operations are performed by
the ray/state initialization unit 8920 and ray/box traversal unit
8930. The additional bit "BoxQueryEnable" from the TraceRay Message
is pipelined in the state initializer 8920 (affecting its
compaction across messages), providing an indication of the
BoxQueryEnable setting to each ray/box traversal unit 8930.
[0938] The ray/box traversal unit 8930 stores "BoxQueryEnable" with
each ray, sending this bit as a tag with the initial Ray load
request. When the requested Ray data is returned from the memory
interface, with BoxQueryEnable set, reciprocal computation is
bypassed and instead a different configuration is loaded for all
components in the RayStore (i.e., in accordance with a box rather
than a ray).
[0939] The ray/box traversal unit 8930 pipelines the BoxQueryEnable
bit to the underlying testing logic. In one embodiment, the raybox
data path is modified in accordance with the following
configuration settings. If BoxQueryEnable==1, the box's plane is
not changed as it is change based on the sign of the x, y and z
components of the ray's direction. Checks performed for the ray
which are unnecessary for the raybox are bypassed. For example, it
is assumed that the querying box has no infinite (INF) or
Not-a-Number (NAN) data types so these checks are bypassed in the
data path.
[0940] In one embodiment, before processing by the
hit-determination logic, another add operation is performed to
determine the value lower+radius (basically the t-value from the
hit) and upper-radius. In addition, upon hitting an "Instance Node"
(in a hardware instancing implementation), it does not compute any
transformation but instead launches an intersection shader using a
shader ID in the instance node.
[0941] In one embodiment, when BoxQueryEnable is set, the ray/box
traversal unit 8930 does not perform the NULL shader lookup for any
hit shader. In addition, when BoxQueryEnable is set, when a valid
node is of the QUAD, MESHLET type, the ray/box traversal unit 8930
invokes an intersection shader just as it would invoke an ANY HIT
SHADER after updating the potential hit information in memory.
[0942] In one embodiment, a separate set of the various components
illustrated in FIG. 89A are provided in each multi-core group 3100A
(e.g., within the ray tracing cores 3150). In this implementation,
each multi-core group 3100A can operate in parallel on a different
set of ray data and/or box data to perform traversal and
intersection operations as described herein.
Apparatus and Method for Meshlet Compression and Decompression for
Ray Tracing
[0943] As described above, a "meshlet" is a subset of a mesh
created through geometry partitioning which includes some number of
vertices (e.g., 16, 32, 64, 256, etc) based on the number of
associated attributes. Meshlets may be designed to share as many
vertices as possible to allow for vertex re-use during rendering.
This partitioning may be pre-computed to avoid runtime processing
or may be performed dynamically at runtime each time a mesh is
drawn.
[0944] One embodiment of the invention performs meshlet compression
to reduce the storage requirements for the bottom level
acceleration structures (BLASs). This embodiment takes advantage of
the fact that a meshet represents a small piece of a larger mesh
with similar vertices, to allow efficient compression within a 128B
block of data. Note, however, that the underlying principles of the
invention are not limited to any particular block size.
[0945] Meshlet compression may be performed at the time the
corresponding bounding volume hierarchy (BVH) is built and
decompressed at the BVH consumption point (e.g., by the ray tracing
hardware block). In certain embodiments described below, meshlet
decompression is performed between the L1 cache (sometimes "LSC
Unit") and the ray tracing cache (sometimes "RTC Unit"). As
described herein, the ray tracing cache is a high speed local cache
used by the ray traversal/intersection hardware.
[0946] In one embodiment, meshlet compression is accelerated in
hardware. For example, if the execution unit (EU) path supports
decompression (e.g., potentially to support traversal shader
execution), meshlet decompression may be integrated in the common
path out of the L1 cache.
[0947] In one embodiment, a message is used to initiate meshlet
compression to 128B blocks in memory. For example, a 4.times.64B
message input may be compressed to a 128B block output to the
shader. In this implementation, an additional node type is added in
the BVH to indicate association with a compressed meshlet.
[0948] FIG. 89B illustrates one particular implementation for
meshlet compression including a meshlet compression block (RTMC)
9030 and a meshlet decompression block (RTMD) 9090 integrated
within the ray tracing cluster. Meshlet compression 9030 is invoked
when a new message is transmitted from an execution unit 8910
executing a shader to the ray tracing cluster (e.g., within a ray
tracing core 3150). In one embodiment, the message includes four
64B phases and a 128B write address. The message from the EU 8910
instructs the meshlet compression block 9030 where to locate the
vertices and related meshet data in local memory 3198 (and/or
system memory depending on the implementation). The meshlet
compression block 9030 then performs meshlet compression as
described herein. The compressed meshlet data may then be stored in
the local memory 3198 and/or ray tracing cache 8960 via the memory
interface 9095 and accessed by the instance/quad intersection
tester 8940 and/or a traversal/intersection shader.
[0949] In FIG. 89B, meshlet gather and decompression block 9090 may
gather the compressed data for a meshlet and decompress the data
into multiple 64B blocks. In one implementation, only decompressed
meshlet data is stored within the L1 cache 8970. In one embodiment,
meshlet decompression is activated while fetching the BVH node data
based on the node-type (e.g., leaf node, compressed) and
primitive-ID. The traversal shader can also access the compressed
meshlet using the same semantics as the rest of the ray tracing
implementation.
[0950] In one embodiment, the meshlet compression block 9030
accepts an array of input triangles from an EU 8910 and produces a
compressed 128B meshlet leaf structure. A pair of consecutive
triangles in this structure form a quad. In one implementation, the
EU message includes up to 14 vertices and triangles as indicated in
the code sequence below. The compressed meshlet is written to
memory via memory interface 9095 at the address provided in the
message.
[0951] In one embodiment, the shader computes the bit-budget for
the set of meshlets and therefore the address is provided such that
footprint compression is possible. These messages are initiated
only for compressible meshlets.
TABLE-US-00030 struct CompressMeshletMsg { uint64_t address; //
Header: 128B aligned destination address for the meshlet float
vert_x[14]; // up to 14 vertex coordinates uint32_t vert_x_bits; //
max vertex bits uint32_t numPrims; // Number of triangles (always
even for quads) float vert_y[14]; uint32_t vert_y_bits; // max
vertex bits uint32_t numIdx; // Number of indices float vert_z[14];
uint32_t vert_z_bits; // max vertex bits uint32_t numPrimIDBits;
int32_t primID[14]; // primIDs PrimLeafDesc primLeafDesc; struct {
int8_t idx_x; int8_t idx_y; int8_t idx_z; int8_t last; // 1 if
triangle is last in leaf, 0 otherwise } index[14]; // vertex
indices int32_t pad0; int32_t pad1; }
[0952] In one embodiment, the meshlet decompression block 9090
decompresses two consecutive quads (128B) from a 128B meshlet and
stores the decompressed data in the L1 cache 8970. The tags in the
L1 cache 8970 track the index of each decompressed quad (including
the triangle index) and the meshlet address. The ray tracing cache
8960 as well as an EU 8910 can fetch a 64B decompressed quad from
the L1 cache 8970. In one embodiment, an EU 8910 fetches a
decompressed quad by issuing a MeshletQuadFetch message to the L1
cache 8960 as shown below. Separate messages may be issued for
fetching the first 32 bytes and the last 32 bytes of the quad.
[0953] Shaders can access triangle vertices from the quad structure
as shown below. In one embodiment, the "if" statements are replaced
by "sel" instructions.
TABLE-US-00031 //Assuming vertex i is a constant determined by the
compiler float3 getVertexi(Quad& q, int triID, int vertexID) {
if (triID == 0) return quad.vi; else if (i == j0) return quad.v0;
else if (i == j1) return quad.v1; else if (i == j2) return quad.v2;
}
[0954] In one embodiment, the ray tracing cache 8960 can fetch a
decompressed quad directly from the L1 cache 8970 bank by providing
the meshlet address and quad index.
TABLE-US-00032 GetQuad Data { uint1_t msb; //MS 32B or LS 32B
uint4_t triangle_idx; // index of the triangle inside the meshlet.
always even for quads. uint64_t meshlet_addr; }
Meshlet Compression Process
[0955] After allocating bits for a fixed overhead such as geometric
properties (e.g., flags and masks), data of the meshlet is added to
the compressed block while computing the remaining bit-budget based
on deltas on (pos.x, pos.y, pos.z) compared to (base.x, base.y,
base.z) where the base values comprise the position of the first
vertex in the list. Similarly prim-ID deltas may be computed as
well. Since the delta is compared to the first vertex, it is
cheaper to decompress with low latency. The base position and
primIDs are part of the constant overhead in the data structure
along with the width of the delta bits. For remaining vertices of
an even number triangles, position deltas and prim-ID deltas are
stored on different 64B blocks in order to pack them in
parallel.
[0956] Using these techniques, the BVH build operation consumes
lower bandwidth to memory upon writing out the compressed data via
the memory interface 9095. In addition, in one embodiment, storing
the compressed meshlet in the L3 cache allows for storage of more
BVH data with the same L3 cache size. In one working
implementation, more than 50% meshlets are compressed 2:1. While
using a BVH with compressed meshlets, bandwidth savings at the
memory results in power savings.
Apparatus and Method for Bindless Thread Dispatching and
Workgroup/Thread Preemption in a Compute and Ray Tracing
Pipeline
[0957] As described above, bindless thread dispatch (BTD) is a way
of solving the SIMD divergence issue for Ray Tracing in
implementations which do not support shared local memory (SLM) or
memory barriers.
[0958] Embodiments of the invention include support for generalized
BTD which can be used to address SIMD divergence for various
compute models. In one embodiment, any compute dispatch with a
thread group barrier and SLM can spawn a bindless child thread and
all of the threads can be regrouped and dispatched via BTD to
improve efficiency. In one implementation, one bindless child
thread is permitted at a time per parent and the originating
threads are permitted to share their SLM space with the bindless
child threads. Both SLM and barriers are released only when finally
converged parents terminate (i.e., perform EOTs). One particular
embodiment allows for amplification within callable mode allowing
tree traversal cases with more than one child being spawned.
[0959] FIG. 90 graphically illustrates an initial set of threads
9000 which may be processed synchronously by the SIMD pipeline. For
example, the threads 9000 may be dispatched and executed
synchronously as a workgroup. In this embodiment, however, the
initial set of synchronous threads 9000 may generate a plurality of
diverging spawn threads 9001 which may produce other spawn threads
9011 within the asynchronous ray tracing architectures described
herein. Eventually, converging spawn threads 9021 return to the
original set of threads 9000 which may then continue synchronous
execution, restoring the context as needed in accordance with the
tracking array 5249.
[0960] In one embodiment, a bindless thread dispatch (BTD) function
supports SIMD16 and SIMD32 modes, variable general purpose register
(GPR) usage, shared local memory (SLM), and BTD barriers by
persisting through the resumption of the parent thread following
execution and completion (post-diverging and then converging
spawn). One embodiment of the invention includes a hardware-managed
implementation to resume the parent threads and a software-managed
dereference of the SLM and barrier resources.
[0961] In one embodiment of the invention, the following terms have
the following meanings:
[0962] Callable Mode: Threads that are spawned by bindless thread
dispatch are in "Callable Mode." These threads can access the
inherited shared local memory space and can optionally spawn a
thread per thread in the callable mode. In this mode, threads do
not have access to the workgroup-level barrier.
[0963] Workgroup (WG) Mode: When threads are executing in the same
manner with constituent SIMD lanes as dispatched by the standard
thread dispatch, they are defined to be in the workgroup mode. In
this mode, threads have access to workgroup-level barriers as well
as shared local memory. In one embodiment, the thread dispatch is
initiated in response to a "compute walker" command, which
initiates a compute-only context.
[0964] Ordinary Spawn: Also referred to as regular spawn threads
9011 (FIG. 90), ordinary spawn threads are initiated whenever one
callable invokes another. Such spawned threads are considered in
the callable mode.
[0965] Diverging Spawn: As shown in FIG. 90, diverging spawn
threads 9001 are triggered when a thread transitions from workgroup
mode to callable mode. A divergent spawn's arguments are the SIMD
width and fixed function thread ID (FFTID), which are
subgroup-uniform.
[0966] Converging Spawn: Converging spawn threads 9021 are executed
when a thread transitions from callable mode back to workgroup
mode. A converging spawn's arguments are a per-lane FFTID, and a
mask indicating whether or not the lane's stack is empty. This mask
must be computed dynamically by checking the value of the per-lane
stack pointer at the return site. The compiler must compute this
mask because these callable threads may invoke each other
recursively. Lanes in a converging spawn which do not have the
convergence bit set will behave like ordinary spawns.
[0967] Bindless thread dispatch solves the SIMD divergence issue
for ray tracing in some implementations which do not allow shared
local memory or barrier operations. In addition, in one embodiment
of the invention, BTD is used to address SIMD divergence using a
variety of compute models. In particular, any compute dispatch with
a thread group barrier and shared local memory can spawn bindless
child threads (e.g., one child thread at a time per parent) and all
the same threads can be regrouped and dispatched by BTD for better
efficiency. This embodiment allows the originating threads to share
their shared local memory space with their child threads. The
shared local memory allocations and barriers are released only when
finally converged parents terminate (as indicated by end of thread
(EOT) indicators). One embodiment of the invention also provides
for amplification within callable mode, allowing tree traversal
cases with more than one child being spawned.
[0968] Although not so limited, one embodiment of the invention is
implemented on a system where no support for amplification is
provided by any SIMD lane (i.e., allowing only a single outstanding
SIMD lane in the form of diverged or converged spawn thread). In
addition, in one implementation, the 32b of (FFTID, BARRIER_ID,
SLM_ID) is sent to the BTD-enabled dispatcher 8950 upon dispatching
a thread. In one embodiment, all these spaces are freed up prior to
launching the threads and sending this information to the bindless
thread dispatcher 8950. Only a single context is active at a time
in one implementation. Therefore, a rogue kernel even after
tempering FFTID cannot access the address space of the other
context.
[0969] In one embodiment, if StackID allocation is enabled, shared
local memory and barriers will no longer be dereferenced when a
thread terminates. Instead, they are only dereferenced if all
associated StackIDs have been released when the thread terminates.
One embodiment prevents fixed-function thread ID (FFTID) leaks by
ensuring that StackIDs are released properly.
[0970] In one embodiment, barrier messages are specified to take a
barrier ID explicitly from the sending thread. This is necessary to
enable barrier/SLM usage after a bindless thread dispatch call.
[0971] FIG. 91 illustrates one embodiment of an architecture for
performing bindless thread dispatching and thread/workgroup
preemption as described herein. The execution units (EU) 8910 of
this embodiment support direct manipulation of the thread execution
mask 9150-9153 and each BTD spawn message supports FFTID reference
counting for re-spawning of a parent thread following completion of
converging spawn 9021. Thus, the ray tracing circuitry described
herein supports additional message variants for BTD spawn and
TraceRay messages. In one embodiment, the BTD-enabled dispatcher
8950 maintains a per-FFTID (as assigned by thread dispatch) count
of original SIMD lanes on diverging spawn threads 9001 and counts
down for converging spawn threads 9021 to launch the resumption of
the parent threads 9000.
[0972] Various events may be counted during execution including,
but not limited to, regular spawn 9011 executions; diverging spawn
executions 9001; converging spawn events 9021; a FFTID counter
reaching a minimum threshold (e.g., 0); and loads performed for
(FFTID, BARRIER_ID, SLM_ID).
[0973] In one embodiment, shared local memory (SLM) and barrier
allocation are allowed with BTD-enabled threads (i.e., to honor
ThreadGroup semantics). The BTD-enabled thread dispatcher 8950
decouples the FFTID release and the barrier ID release from the end
of thread (EOT) indications (e.g., via specific messages).
[0974] In one embodiment, in order to support callable shaders from
compute threads, a driver-managed buffer 9170 is used to store
workgroup information across the bindless thread dispatches. In one
particular implementation, the driver-managed buffer 9170 includes
a plurality of entries, with each entry associated with a different
FFTID.
[0975] In one embodiment, within the state initializer 8920, two
bits are allocated to indicate the pipeline spawn type which is
factored in for message compaction. For diverging messages, the
state initializer 8920 also factors in the FFTID from the message
and pipelines with each SIMD lane to the ray/box traversal block
8930 or bindless thread dispatcher 8950. For converging spawn 9021,
there is an FFTID for each SIMD lane in the message and pipeline
FFTID with each SIMD lane for the ray/box traversal unit 8930 or
bindless thread dispatcher 8950. In one embodiment, the ray/box
traversal unit 8930 also pipelines the spawn type, including
converging spawn 9021. In particular, in one embodiment, the
ray/box traversal unit 8930 pipelines and stores the FFTID with
every ray converging spawn 9021 for TraceRay messages.
[0976] In one embodiment, the thread dispatcher 8950 has a
dedicated interface to provide the following data structure in
preparation for dispatching a new thread with the bindless thread
dispatch enable bit set:
TABLE-US-00033 Struct tsl_sts_inf { // non-stallable interface
Logic[8] FFTID; Logic[8] BARRIER_ID; Logic[8] SLM_ID; Logic[8]
count_valid_simd_lanes; }
[0977] The bindless thread dispatcher 8950 also processes the end
of thread (EOT) message with three additional bits: Release_FFTID,
Release_BARRIER_ID, Release_SLM_ID. As mentioned, the end of thread
(EOT) message does not necessarily release/dereference all the
allocations associated with the IDs, but only the allocations with
a release bit set. A typical use-case is when a diverging spawn
9001 is initiated, the spawning thread produces an EOT message but
the release bit is not set. Its continuation after the converging
spawn 9021 will produce another EOT message, but this time with the
release bit set. Only at this stage will all the per-thread
resources be recycled.
[0978] In one embodiment, the bindless thread dispatcher 8950
implements a new interface to load the FFTID, BARRIER_ID, SLM_ID
and the lane count. It stores all of this information in an
FFTID-addressable storage 9121 that is a certain number of entries
deep (max_fftid, 144 entries deep in one embodiment). In one
implementation, the BTD-enabled dispatcher 8950, in response to any
regular spawn 9011 or diverging spawn 9001, uses this identifying
information for each SIMD lane, performs queries to the
FFTID-addressable storage 9121 on a per-FFTID basis, and stores the
thread data in the sorting buffer as described above (see, e.g.,
content addressable memory 4201 in FIG. 42). This results in
storing an additional amount of data (e.g., 24 bits) in the sorting
buffer 4201 per SIMD lane.
[0979] Upon receiving a converging spawn message, for every SIMD
lane from the state initializer 8920 or ray/box traversal block
8930 to the bindless thread dispatcher 8950, the per-FFTID count is
decremented. When a given parent's FFTID counter becomes zero, the
entire thread is scheduled with original execution masks 9150-9153.
A continuation shader record 4201 is provided by the converging
spawn message in the sorting circuitry 4008.
[0980] Different embodiments of the invention may operate in
accordance with different configurations. For example, in one
embodiment, all diverging spawns 9001 performed by a thread must
have matching SIMD widths. In addition, in one embodiment, a SIMD
lane must not perform a converging spawn 9021 with the
ConvergenceMask bit set within the relevant execution mask
9150-9153 unless some earlier thread performed a diverging spawn
with the same FFTID. If a diverging spawn 9001 is performed with a
given StackID, a converging spawn 9021 must occur before the next
diverging spawn.
[0981] If any SIMD lane in a thread performs a diverging spawn,
then all lanes must eventually perform a diverging spawn. A thread
which has performed a diverging spawn may not execute a barrier, or
deadlock will occur. This restriction is necessary to enable spawns
within divergent control flow. The parent subgroup cannot not be
respawned until all lanes have diverged and reconverged.
[0982] A thread must eventually terminate after performing any
spawn to guarantee forward progress. If multiple spawns are
performed prior to thread termination, deadlock may occur. In one
particular embodiment, the following invariants are followed,
although the underlying principles of the invention are not so
limited: [0983] All diverging spawns performed by a thread must
have matching SIMD widths. [0984] A SIMD lane must not perform a
converging spawn with the ConvergenceMask bit set within the
relevant execution mask 9150-9153 unless some earlier thread
performed a diverging spawn with the same FFTID. [0985] If a
diverging spawn is performed with a given stackID, a converging
spawn must occur before the next diverging spawn. [0986] If any
SIMD lane in a thread performs a diverging spawn, then all lanes
must eventually perform a diverging spawn. A thread which has
performed a diverging spawn may not execute a barrier, or deadlock
will occur. This restriction enables spawns within divergent
control flow. The parent subgroup cannot not be respawned until all
lanes have diverged and reconverged. [0987] A thread must
eventually terminate after executing any spawn to guarantee forward
progress. If multiple spawns are performed prior to thread
termination, deadlock may occur.
[0988] In one embodiment, the BTD-enabled dispatcher 8950 includes
thread preemption logic 9120 to preempt the execution of certain
types of workloads/threads to free resources for executing other
types of workloads/threads. For example, the various embodiments
described herein may execute both compute workloads and graphics
workloads (including ray tracing workloads) which may run at
different priorities and/or have different latency requirements. To
address the requirements of each workload/thread, one embodiment of
the invention suspends ray traversal operations to free execution
resources for a higher priority workload/thread or a
workload/thread which will otherwise fail to meet specified latency
requirements.
[0989] As described above with respect to FIGS. 52A-B, one
embodiment reduces the storage requirements for traversal using a
short stack 5203-5204 to store a limited number of BVH nodes during
traversal operations. These techniques may be used by the
embodiment in FIG. 91, where the ray/box traversal unit 8930
efficiently pushes and pops entries to and from the short stack
5203-5204 to ensure that the required BVH nodes 5290-5291 are
available. In addition, as traversal operations are performed,
traversal/stack tracker 5248 updates the tracking data structure,
referred to herein as the tracking array 5249, as well as the
relevant stacks 5203-5204 and ray tracing data 4902. Using these
techniques, when traversal of a ray is paused and restarted, the
traversal circuitry/logic 8930 can consult the tracking data
structure 5249 and access the relevant stacks 5203-5204 and ray
tracing data 4902 to begin traversal operations for that ray at the
same location within the BVH where it left off.
[0990] In one embodiment, the thread preemption logic 9120
determines when a set of traversal threads (or other thread types)
are to be preempted as described herein (e.g., to free resources
for a higher priority workload/thread) and notifies the ray/box
traversal unit 8930 so that it can pause processing one of the
current threads to free resources for processing the higher
priority thread. In one embodiment, the "notification" is simply
performed by dispatching instructions for a new thread before
traversal is complete on an old thread.
[0991] Thus, one embodiment of the invention includes hardware
support for both synchronous ray tracing, operating in workgroup
mode (i.e., where all threads of a workgroup are executed
synchronously), and asynchronous ray tracing, using bindless thread
dispatch as described herein. These techniques dramatically improve
performance compared to current systems which require all threads
in a workgroup to complete prior to performing preemption. In
contrast, the embodiments described herein can perform stack-level
and thread-level preemption by closely tracking traversal
operation, storing only the data required to restart, and using
short stacks when appropriate. These techniques are possible, at
least in part, because the ray tracing acceleration hardware and
execution units 8910 communicate via a persistent memory structure
3198 which is managed at the per-ray level and per-BVH level.
[0992] When a Traceray message is generated as described above and
there is a preemption request, the ray traversal operation may be
preempted at various stages, including (1) not yet started, (2)
partially completed and preempted, (3) traversal complete with no
bindless thread dispatch, and (4) traversal complete but with a
bindless thread dispatch. If the traversal is not yet started, then
no additional data is required from the tracking array 5249 when
the raytrace message is resumed. If the traversal was partially
completed, then the traversal/stack tracker 5248 will read the
tracking array 5249 to determine where to resume traversal, using
the ray tracing data 4902 and stacks 5121 as required. It may query
the tracking array 5249 using the unique ID assigned to each
ray.
[0993] If the traversal was complete, and there was no bindless
thread dispatch, then a bindless thread dispatch may be scheduled
using any hit information stored in the tracking array 5249 (and/or
other data structures 4902, 5121). If traversal completed and there
was a bindless thread dispatch, then the bindless thread is
restored and execution is resumed until complete.
[0994] In one embodiment, the tracking array 5249 includes an entry
for each unique ray ID for rays in flight and each entry may
include one of the execution masks 9150-9153 for a corresponding
thread. Alternatively, the execution masks 9150-9153 may be stored
in a separate data structure. In either implementation, each entry
in the tracking array 5249 may include or be associated with a
1-bit value to indicate whether the corresponding ray needs to be
resubmitted when the ray/box traversal unit 8930 resumes operation
following a preemption. In one implementation, this 1-bit value is
managed within a thread group (i.e., a workgroup). This bit may be
set to 1 at the start of ray traversal and may be reset back to 0
when ray traversal is complete.
[0995] The techniques described herein allow traversal threads
associated with ray traversal to be preempted by other threads
(e.g., compute threads) without waiting for the traversal thread
and/or the entire workgroup to complete, thereby improving
performance associated with high priority and/or low latency
threads. Moreover, because of the techniques described herein for
tracking traversal progress, the traversal thread can be restarted
where it left off, conserving a significant processing cycles and
resource usage. In addition, the above-described embodiments allow
a workgroup thread to spawn a bindless thread and provides
mechanisms for reconvergence to arrive back to the original SIMD
architecture state. These techniques effectively improve
performance for ray tracing and compute threads by an order of
magnitude.
Apparatus and Method for Data-Parallel Ray Tracing
[0996] In scientific visualization (but also in movies and other
domains) data sets are increasingly growing to sizes that cannot be
processed by a single node. For off-line algorithms (mostly in
movies) this is often handled through paging, caching, and
out-of-core techniques; but when an interactive setting is required
(e.g., visualization for oil-and-gas, scientific visualization in a
large-data/HPC environment, interactive movie content previews,
etc) this is no longer possible. In this case, it is absolutely
necessary to use some form of data parallel rendering, in which the
data is partitioned across multiple different nodes--such that the
entirety of the data can be stored across all nodes--and where
these nodes collaborate in rendering the required image.
[0997] The embodiments of the invention include an apparatus and
method for reducing the bandwidth for transferring rays and/or
volume blocks in the context of data-distributed ray tracing across
multiple compute nodes. FIG. 92, for example, illustrates a ray
tracing cluster 9200 comprising a plurality of ray tracing nodes
9210-9213 which perform ray tracing operations in parallel,
potentially combining the results on one of the nodes. In the
illustrated architecture, the ray tracing nodes 9210-9213 are
communicatively coupled to a client-side ray tracing application
9230 via a gateway 9220.
[0998] It will be assumed in the description below that multiple
nodes 9210-9213 jointly hold the ray tracing data. Each such node
9210-9213 may contain one or more CPUs, GPUs, FPGAs, etc, and the
computations may be performed on either individual ones or a
combination of these resources. In one embodiment, the compute
nodes 9210-9213 communicate with one another through some form of
network 9215 such as Infiniband, OmniPath, or NVLink, to name a
few. The data may be portioned across the memories of these nodes
9210-9213, either because the application using the renderer has
itself partitioned the data (as is the case for many in situ
algorithms or parallel middlewares such as ParaView, Visit, etc),
or because the renderer has created this partitioning.
[0999] To do parallel rendering in such an environment, there are a
variety of algorithmic choices: compositing-based approaches have
each node render an image of its local data, and combine these
partial results using depth- and/or alpha compositing. Data
Forwarding (or caching) approaches compute a given ray's (or
pixel's, path's, etc) operations on a given node, detect whenever
this ray/pixel/path needs data that lives on another node, and
fetches this data on demand. Ray Forwarding based approaches do not
forward data to the rays that need it, and instead send the rays to
the node owning the data.
[1000] Among these choices, compositing is the simplest, and most
widely used; however, it is only applicable for relatively simple
rendering effects, and cannot easily be used for effects such as
shadows, reflections, ambient occlusion, global illumination,
volumetric scattering, volumetric shadows, etc. Such effects, which
are being required more frequently by users, require some sort of
ray tracing in which case data parallel rendering either fetches
data to the rays or sends the rays to the data. Both approaches
have been used before and their limitations are well understood. In
particular, both approaches suffer from high bandwidth
requirements, either by sending up to billions of rays around (for
ray forwarding), or by having each node 9210-9213 fetch up to many
gigabytes of data (for data forwarding), or both (when a
combination of both is used).
[1001] Though network bandwidth is rising dramatically, data size
and/or ray count are rising, too, meaning that this bandwidth is,
in practice, very quickly the limiting factor for performance. In
fact, it often is the sole reason that interactive performance
cannot be achieved, except in very simplistic settings (such as
primary-ray only rendering, in which case one could also have used
compositing).
[1002] One embodiment of the invention focuses on the core idea
that, in practice, very large parts of the data often do not
actually matter for a given frame. For example, in volume rendering
the user often uses a "transfer function" to highlight certain
regions of the data, with less interesting data set to fully
transparent. Clearly, a ray that would only traverse
"un-interesting" data would not need to fetch this data (or be sent
to this data), and the respective bandwidth may be saved.
Similarly, for surface-based ray tracing, if a ray passes through a
region of space owned by another node, but does not actually
intersect any triangles there, then it does not actually need to
interact with this other node's triangles.
[1003] One embodiment extends the concepts of "empty space
skipping" and "bounding volumes" from individual nodes to data
parallel rendering, in the form of using what are referred to
herein as "proxies" 9230-9233 for a node's data. In particular,
each node computes a very low memory footprint proxy 9230-9233 of
its own data such that this proxy provides the ability to either
approximate or conservatively bound this data. All nodes 9210-9213
then exchange their proxies 9230-9233 such that each node has every
other node's proxies. For example, the proxies 9230 stored on node
9210 will include proxy data from nodes 9211-9213. When a node
needs to trace a ray through a spatial region owned by another node
it first traces this ray through its own copy of this node's proxy.
If that proxy guarantees that no meaningful interaction will occur,
it can skip sending that ray/fetching that data, thereby saving the
bandwidth required for doing so.
[1004] FIG. 93 illustrates additional details of a ray tracing node
9210 in accordance with one embodiment of the invention. A volume
subdivision module 9265 subdivides a volume into a plurality of
partitions each of which is processed by a different node. Working
data set 9360 comprises the data for the partition to be processed
by node 9210. A proxy generation module 9250 generates a proxy 9340
based on the working data set 9360. The proxy 9340 is transmitted
to each of the other ray tracing nodes 9211-9213 which use the
proxy to cull unneeded data as described herein. Similarly, proxies
9341-9343 generated on nodes 9211-9213, respectively, are
transmitted to node 9210. Ray tracing engine 9315 performs ray
tracing operations using both the working data set 9360 stored
locally and the proxies 9341-9343 provided by each of the
interconnected nodes 9211-9213.
[1005] FIG. 94 illustrates an example in which, in the context of
volume rendering, a given volume data set 9400 is too large to be
rendered on one node, so it gets partitioned into multiple blocks
9401-9404 (in this case, a 2.times.2 set). As illustrated in FIG.
95, this logically partitioned volume may then be distributed
across different nodes 9210-9213, each one retaining part of the
volume.
[1006] Traditionally, every time a node wants to send a ray that
passes through other nodes' spatial regions, it has to either send
this ray to those nodes, or fetch those nodes' data. In FIG. 96,
for example, node 9210 traces a ray that passes through space owned
by nodes 9211-9213.
[1007] As illustrated in FIG. 97, in one embodiment, each node
9210-9213 computes a local proxy 9240-9243 for its part of the data
9401-9404, respectively, where the proxy is any sort of object that
is (significantly) smaller in size, but allows for approximating or
conservatively bounding that node's data. For example, in one
embodiment, each node computes what is commonly known as a
"macrocell grid"; a lower resolution grid where each cell
corresponds to a region of cells in the input volume, and where
each such cell stores, for example, the minimum and maximum scalar
value in that region (in the context of single-node rendering, this
is commonly used for "space skipping"). In the illustrated example,
each node 9210-9213 computes one such proxy 9240-9243 for its part
of the data. In one embodiment, all nodes then exchange their
respective proxies until each node has all proxies for every node,
as illustrated in FIG. 98.
[1008] If, for a given transfer function setting, only some of the
data values are actually interesting (in the sense that they are
not completely transparent), then this can be conservatively
detected in the proxy (just as traditional, single-node space
skipping does). This is illustrated as regions 9940-9943 in FIG.
99.
[1009] In addition, since every node has every other nodes' proxies
each node can also conservatively bound which other nodes' regions
are interesting based on the proxies it has for these nodes, as
shown in FIG. 100. If node 9210 has to trace a ray that straddles
node's 9211-9213's data regions then the ray may be projected onto
the proxy and traversed there, as indicated by the dotted arrow.
This indicates that though the ray does pass through space owned by
nodes 9210-9212, only node 9212 actually contains any interesting
regions, so this ray can be forwarded to node 9212, as indicated in
FIG. 100 by the solid arrow, without processing on nodes 9210 or
sending to node 9211 (or, in a caching context, data may be fetched
only from node 9210 rather than from both 9211 and 9212).
[1010] A method in accordance with one embodiment of the invention
is illustrated in FIG. 101. The method may be implemented within
the context of the architectures described above, but is not
limited to any particular processing or system architecture.
[1011] At 10101, a volume is logically subdivided into a plurality
of partitions (N partitions where N is an integer value) and, at
10102, data associated with the N partitions is distributed to N
different nodes (e.g., one partition per node in one embodiment).
At 10103, each node computes a proxy for its respective partition
and sends the proxy to the other nodes. At 10104,
traversal/intersection operations are performed for a current ray
or group of rays (e.g., a beam) using the proxies, ignoring regions
within the proxies which are not relevant to the operations (e.g.,
regions which are not traversed by the ray). As mentioned, for a
given transfer function setting, only some of the data values are
actually interesting (e.g., because they are not completely
transparent). This may be conservatively detected in the proxy as
done with single-node space skipping. If the ray interacts with the
proxy, determined at 10105, then at 10106, the ray(s) are sent to
the node associated with the proxy or data is retrieved from the
node. The next ray or group of rays are then selected at 10107.
[1012] Of course, the embodiments described herein depend on the
actual data, the ray distribution, the transfer function, etc.
However it is not uncommon for data to look very similar to the
example provided above. Obviously, for data sets/transfer functions
that result in a significantly less "sparse" post-classified data
set (i.e., data set after the transfer function is applied) the
proxies would not help much. In that case, however, the rays would
likely terminate very quickly and therefore do not have to be sent
among nodes very often and do not generate excessive bandwidth. In
essence, the biggest problem cases are those where much of the data
is sparse, and where rays travel across many nodes, and those are
exactly the cases where the techniques described herein are most
effective.
Examples
[1013] The following are example implementations of different
embodiments of the invention
[1014] Example 1. An apparatus comprising: a tesselator to
tessellate an input patch to a grid primitive comprising a
plurality of interconnected quads, each quad comprising two
implicit triangles and sharing at least two vertices with an
adjacent quad; a bounding box generator to construct a bounding box
to bound each quad of the grid primitive to produce a plurality of
bounding boxes corresponding to the plurality of interconnected
quads; and ray traversal hardware logic to determine if a ray
traverses one or more of the plurality of bounding boxes; and
intersection hardware logic to process a bounding box traversed by
the ray to determine if the ray intersects one of the implicit
triangles represented by the quad which is bounded by the bounding
box.
[1015] Example 2. The apparatus of example 1 wherein the grid
primitive comprises an M.times.M matrix of vertices forming the
plurality of interconnect quads.
[1016] Example 3. The apparatus of example 1 wherein the bounding
box generator is integral to the ray traversal hardware logic or a
bounding volume hierarchy (BVH) builder.
[1017] Example 4. The apparatus of example 1 wherein for a grid
primitive comprising N quads, the bounding box generator is to
generate an N-wide BVH node having a child node associated with
each quad.
[1018] Example 5. The apparatus of example 1 wherein a bitmask is
generated based on the grid primitive, each bit in the bitmask
associated with one of the implicit triangles or one of the quads,
wherein if a bit in the bitmask is set to 0, the associated
implicit triangle or quad is considered invalid.
[1019] Example 6. The apparatus of example 1 further comprising:
motion blur hardware logic to interpolate between a first
representation of a first implicit triangle at a first time and a
second representation of the first implicit triangle at a second
time.
[1020] Example 7. The apparatus of example 1 wherein the grid
primitive is one of a plurality of grid primitives, the apparatus
further comprising: compression hardware logic to identify shared
vertices of the plurality of grid primitives and to store only one
set of vertex data for each shared vertex.
[1021] Example 8. The apparatus of example 7 wherein the
compression hardware logic is to generate an index pointing to an
array where the set of vertex data is stored.
[1022] Example 9. The apparatus of example 8 wherein the
compression hardware logic is to identify one or more shared edges
of the implicit triangles, the compression hardware logic to store
a single set of edge data for each shared edge.
[1023] Example 10. A method comprising: tessellating an input patch
to a grid primitive comprising a plurality of interconnected quads,
each quad comprising two implicit triangles and sharing at least
two vertices with an adjacent quad; constructing a bounding box to
bound each quad of the grid primitive to produce a plurality of
bounding boxes corresponding to the plurality of interconnected
quads; and determining if a ray traverses one or more of the
plurality of bounding boxes; and processing a bounding box
traversed by the ray to determine if the ray intersects one of the
implicit triangles represented by the quad which is bounded by the
bounding box.
[1024] Example 11. The method of example 10 wherein the grid
primitive comprises an M.times.M matrix of vertices forming the
plurality of interconnect quads.
[1025] Example 12. The method of example 10 wherein the bounding
box generator is integral to the ray traversal hardware logic
and/or a bounding volume hierarchy (BVH) builder.
[1026] Example 13. The method of example 10 wherein for a grid
primitive comprising N quads, the bounding box generator is to
generate an N-wide BVH node having a child node associated with
each quad.
[1027] Example 14. The method of example 10 wherein a bitmask is
generated based on the grid primitive, each bit in the bitmask
associated with one of the implicit triangles or one of the quads,
wherein if a bit in the bitmask is set to 0, the associated
implicit triangle or quad is considered invalid.
[1028] Example 15. The method of example 10 a first representation
of a first implicit triangle at a first time and a second
representation of the first implicit triangle at a second time.
[1029] Example 16. The method of example 10 wherein the grid
primitive is one of a plurality of grid primitives, the method
further comprising: identifying shared vertices of the plurality of
grid primitives and storing only one set of vertex data for each
shared vertex.
[1030] Example 17. The method of example 16 further comprising:
generating an index pointing to an array where the set of vertex
data is stored.
[1031] Example 18. The method of example 17 further comprising:
identifying one or more shared edges of the implicit triangles, and
storing only a single set of edge data for each shared edge.
[1032] Example 19. A machine-readable medium having program code
stored thereon which, when executed by a machine, causes the
machine to perform the operations of: tessellating an input patch
to a grid primitive comprising a plurality of interconnected quads,
each quad comprising two implicit triangles and sharing at least
two vertices with an adjacent quad; constructing a bounding box to
bound each quad of the grid primitive to produce a plurality of
bounding boxes corresponding to the plurality of interconnected
quads; and determining if a ray traverses one or more of the
plurality of bounding boxes; and processing a bounding box
traversed by the ray to determine if the ray intersects one of the
implicit triangles represented by the quad which is bounded by the
bounding box.
[1033] Example 20. The machine-readable medium of example 19
wherein the grid primitive comprises an M.times.M matrix of
vertices forming the plurality of interconnect quads.
[1034] Example 21. The machine-readable medium of example 19
wherein the bounding box generator is integral to the ray traversal
hardware logic and/or a bounding volume hierarchy (BVH)
builder.
[1035] Example 22. The machine-readable medium of example 19
wherein for a grid primitive comprising N quads, the bounding box
generator is to generate an N-wide BVH node having a child node
associated with each quad.
[1036] Example 23. The machine-readable medium of example 19
wherein a bitmask is generated based on the grid primitive, each
bit in the bitmask associated with one of the implicit triangles or
one of the quads, wherein if a bit in the bitmask is set to 0, the
associated implicit triangle or quad is considered invalid.
[1037] Example 24. The machine-readable medium of example 19
further comprising program code to cause the machine to perform the
operations of: interpolating between a first representation of a
first implicit triangle at a first time and a second representation
of the first implicit triangle at a second time.
[1038] Example 25. The machine-readable medium of example 19
wherein the grid primitive is one of a plurality of grid
primitives, the machine-readable medium further comprising program
code to cause the machine to perform the operations of: identifying
shared vertices of the plurality of grid primitives and storing
only one set of vertex data for each shared vertex.
[1039] Embodiments of the invention may include various steps,
which have been described above. The steps may be embodied in
machine-executable instructions which may be used to cause a
general-purpose or special-purpose processor to perform the steps.
Alternatively, these steps may be performed by specific hardware
components that contain hardwired logic for performing the steps,
or by any combination of programmed computer components and custom
hardware components.
[1040] As described herein, instructions may refer to specific
configurations of hardware such as application specific integrated
circuits (ASICs) configured to perform certain operations or having
a predetermined functionality or software instructions stored in
memory embodied in a non-transitory computer readable medium. Thus,
the techniques shown in the figures can be implemented using code
and data stored and executed on one or more electronic devices
(e.g., an end station, a network element, etc.). Such electronic
devices store and communicate (internally and/or with other
electronic devices over a network) code and data using computer
machine-readable media, such as non-transitory computer
machine-readable storage media (e.g., magnetic disks; optical
disks; random access memory; read only memory; flash memory
devices; phase-change memory) and transitory computer
machine-readable communication media (e.g., electrical, optical,
acoustical or other form of propagated signals--such as carrier
waves, infrared signals, digital signals, etc.).
[1041] In addition, such electronic devices typically include a set
of one or more processors coupled to one or more other components,
such as one or more storage devices (non-transitory
machine-readable storage media), user input/output devices (e.g., a
keyboard, a touchscreen, and/or a display), and network
connections. The coupling of the set of processors and other
components is typically through one or more busses and bridges
(also termed as bus controllers). The storage device and signals
carrying the network traffic respectively represent one or more
machine-readable storage media and machine-readable communication
media. Thus, the storage device of a given electronic device
typically stores code and/or data for execution on the set of one
or more processors of that electronic device. Of course, one or
more parts of an embodiment of the invention may be implemented
using different combinations of software, firmware, and/or
hardware. Throughout this detailed description, for the purposes of
explanation, numerous specific details were set forth in order to
provide a thorough understanding of the present invention. It will
be apparent, however, to one skilled in the art that the invention
may be practiced without some of these specific details. In certain
instances, well known structures and functions were not described
in elaborate detail in order to avoid obscuring the subject matter
of the present invention. Accordingly, the scope and spirit of the
invention should be judged in terms of the claims which follow.
* * * * *